Is not Champion OP when compared to Mage Knight, Storm Warrior and possibly Psychic Warrior?
I know that balance varies between classes, modules and party composition, but lets take a look at details to see what I mean.
Defense (HP/Saves/AC).
Champion - 10 HD, 1 Save (Fortitude), all armors and shields, Divine Shield feat for casting with heavy/tower shields.
Mage Knight - 8 HD, 2 Saves (Reflex, Will), light armors and shields, Armored Casting feat + 1-2 armor proficiency feats for casting with medium/heavy armors, no heavier shields.
Storm Warrior - 10 HD, 1 Save (Fortitude), casting only with leather/hide (non metal) armors and light shields.
Psychic Warrior - 8 HD, 1 Save (Fortitude), all armors and light/heavy shields, tower shield proficiency feat for casting with it.
HD is random (possible average 1 HP advantage per level), Constitution guarantees HP, and Saves are valuable (average of two abilities divided by 2, so actually ability 4 means +1 save) for less damage/useless/ineffective.
I would say ok, Mage Knight wins, because armor can be upgraded with more available bonus feats (2-3).
Champion comparison is 2 HD (possible average 1 HP advantage per level) vs +1 Save.
Psychic Warrior has lower both, HP and Save, while Storm Warrior only save, but is additionally limited in AC (non metal armors).
Melee.
Champion - 4 BAB, class feats: Perfect Combat Casting, Divine Weapon (x2, bypassing aligned DR, +2/+5 damage holy/unholy/axiomatic/anarchic).
Mage Knight - 4 BAB, class feats: Perfect Combat Casting, Elemental Weapon (x2, any elemental weapon +1d6/+2d6).
Storm Warrior - 4 BAB, class feats: Perfect Combat Casting, Storm Weapon (x2, only electric weapon +1d6/+2d6), Water/Forest Affinity (+2 attack and AC when underwater/swimming or forest/jungle).
Psychic Warrior - 3 BAB, class feats: Strength Focus (+2 grapple and strength checks), Melee Focus (+1 melee attack).
All classes can choose 3 weapon proficiences.
Perfect Combat Casting feat gives +4 Concentration, ignores attacks of opportunity when casting, and is available to all except Psychic Warrior.
Basic Attack Bonus (BAB) increases number of attacks to up to 4 (3 if 3 BAB, attacks above 1 require full round attack) and their bonus to hit up to +20/+15/+10/+5 (+15/+10/+5 if 3 BAB), what makes Psychic Warrior less effective in it.
Champion and Mage Knight seem similar in class melee feats, while two others offer different type of benefits (except weaker Storm Weapon).
I would say Champion and Mage Knight are winners here.
Storm Warrior has situational class feats (only electric weapon or specific environment bonus), and then Psychic Warrior with 3 BAB has less attacks and chances to hit.
Spellcasting.
Champion - 7th Cleric spells (wisdom), new spell level per 2-3 levels, 4 slots (28 total), new slot in each spell level per 1/1-2/4 levels, 41 of 125 spells, scrolls to learn or cast.
Mage Knight - 6th Wizard spells (intellect), new spell level per 3 levels, 3 slots (18 total), new slot in each spell level per 1/7-8 levels, 41 of 214 spells, scrolls to learn or cast.
Storm Warrior - 7th Druid spells (wisdom), new spell level per 2-3 levels, 4 slots (28 total), new slot in each spell level per 1/1-2/4 levels, 41 of 97 spells, scrolls to learn or cast.
Psychic Warrior - 6th class powers (wisdom), new spell level per 3 levels, new 2/4/8/12 power points per 5 levels (127 total), 31 powers known of 48.
Champion class feats: Perfect Combat Casting, Spell Focus (x2, +1/+2 DC to all spells), Energy Defence (4 Protection From Energy spells as move).
Mage Knight class feats: Perfect Combat Casting, Spell Focus (x2 5, +1/+2 DC to 1 of 5 spell schools), Unlimited Spells (12 damage spells get +2 damage and no level limit, 10 are Evocation), Enhance Ability (x2, 2 spells get +2 bonus, then as move).
Storm Warrior class feats: Perfect Combat Casting, Spell Focus (x2, +1/+2 DC to all spells).
Psychic Warrior class feats: Psionic Talent (+1 power points per level), Psychometabolism (x2, 11/22 powers as move), Biofeedback/Mind Leech (improvements to single powers).
Champion and Storm Warrior seem similar, except that the second has no improvement to specific spells and spell list is lower by 28, giving 97 instead of 125.
Mage Knight is a noticeable disappointment here, not only because max spell level is lower by 1 (3 total), but also number of slots (max 3 per spell level and 18 total, instead of 4 and 28, giving difference of 1 and 10) and progression in getting them is lower too (new spell level per 3 levels instead of 2-3, third slot after 7-8 more levels instead of 1-2).
Additionally, Spell Focus feat is divided into 5 categories of spells instead of 1 like in other classes (yes, I know, it is arcane vs divine standard) and Unlimited Spells seems to be not enough useful, because of mentioned earlier limits.
Psychic Warrior seems to be harder for direct comparison for me, since this class works in some different way.
Feats and Skills.
Champion - 5 bonus feats, honor skill, other class feats: Divine Armor (ignores lower speed with medium/heavy armors).
Mage Knight - 8 bonus feats, arcana skill, other class feats: nothing extra except already mentioned.
Storm Warrior - 5 bonus feats, nature skill, other class feats: Fire/Cold/Electricity Resistance (10 DR).
Psychic Warrior - 8 bonus feats, psionics skill, other class feats: nothing extra except already mentioned.
Mage Knight has 8 bonus feats, but 2-3 can be needed for casting in medium/heavy armors (so 5-6), while Psychic Warrior can use them for other things.
Champion has probably less useful skill, but Divine Armor might be something to consider when using heavy armor without additional bonus speed item.
Warrior focused.
Champion and Mage Knight seem to be similar as frontline warrior, if second one use 2-3 bonus feats for Armored Casting and armor proficiency, so they end up with 5 vs 5-6 bonus feats for other things.
To compare, pure Fighter class has 31 bonus feats, 5 weapon proficiences, and 23 warrior focused class feats.
They can be good enough melee frontliners with useful support spells (no DC ones), as long as they focus all their limited number of feats on that part, keep maximizing Strength (melee, maneuvers, checks, ranged, save, feats, weight) as priority (18-20 starter ability + items + each level up), improve Constitution (hp, save, concentration) and Dexterity (ranged, ac, opportunities, save, feats, initiative) as secondary (14-18 starter abilities + optional items), and ignore Intelligence/Wisdom/Charisma (8-12 starter abilities + no items except bonus slot ones, spells can be learn from scrolls, there are many useful spells with no DC, bonus spell slots per attribute is low).
Storm Warrior and Psychic Warrior seem to be weaker, one limited to leather/hide armors, second with 8 HD and 3 BAB.
Spellcasting Focused.
As mentioned earlier, Champion and Storm Warrior seem to be similar as spellcaster, while Mage Knight is a noticeable disappointment.
To compare, pure Cleric/Druid/Wizard has 9th spells, new spell level per 2 levels, 4-5/4-5/4 slots (41/41/36 total), new slot in each spell level per 1/2/3/4 levels.
It seems like Champion is good as both, warrior and weaker spellcaster.
Mage Knight is good as warrior, but noticeably weaker as spellcaster.
Storm Warrior is good as weaker spellcaster, but weaker warrior than two others.
Psychic Warrior is weaker warrior, but I am not sure about comparing as spellcaster.
List of quick comparison view on all classes.
Maybe someone will find it useful.
Fighter (warrior, 10 HD, 31 bonus feats + 5/int weapons, 23 class feats, 4 BAB, armors/shields, warrior/streetwise)
Gladiator (warrior, 12 HD, 8 bonus feats + all weapons, 16 class feats, 4 special abilities, 4 BAB, armors/shields, warrior)
Death Knight (warrior, 10 HD, 2 saves, 2 bonus feats + 4 weapons, 12 class feats, 8 special abilities, 4 BAB, armors/shields, assassin)
Monk (warrior, 8 HD, 3 saves, 5 bonus feats + light/natural weapons, 11 class feats, 13 special abilities, 3 BAB or 5 special attacks, religion/assassin/poison)
Samurai (warrior, 10 HD, 4 bonus feats + sword/1/wis weapons, 13 class feats, 6 special abilities, 4 BAB, armors, honor)
Barbarian (warrior, 12 HD, 4 bonus feats + 4 weapons, 12 class feats, 9 special abilities, 4 BAB, light/medium armors and all shields, warrior)
Champion (warrior/Cleric, 10 HD, 5 bonus feats + 3 weapons, 8 class feats, 7th wis cleric spells, 41/wis spells of 125, 4 slots of 28/wis, 4 BAB, armors/shields, honor)
Mage Knight (warrior/Wizard, 8 HD, 2 saves, 8 bonus feats + 3 weapons, 17 class feats, 6th int wizard spells, 41/int spells of 214, 3 slots of 18/int, 4 BAB, light armors/shields, arcana)
Storm Warrior (warrior/Druid, 10 HD, 5 bonus feats + 3 weapons, 10 class feats, 7th wis druid spells, 41/wis spells of 97, 4 slots of 28/wis, 4 BAB, leather/hide armors and light shields, nature)
Psychic Warrior (warrior/Psionicist, 8 HD, 8 bonus feats + 3 weapons, 8 class feats, 6th wis class powers, 31/wis powers of 48, 127/wis PP, 3 BAB, all armors and light/heavy shields, psionics)
Paladin (warrior/Cleric, 10 HD, 5 bonus feats + 3 weapons, 10 class feats, 5 special abilities, 4th wis class spells, 36 spells, 3 slots of 12/wis, 4 BAB, armors/shields, honor/detect)
Ranger (warrior/Druid, 10 HD, 2 saves, 5 bonus feats + 3 weapons, 9 class feats, 8 special abilities, 4th wis class spells, 26 spells, 3 slots of 12/wis, 4 BAB, light armors/shields, nature/wilderness)
Rogue (warrior/Wizard, 8 HD, 3 bonus feats + 3 weapons, 8 class feats, 9 special abilities, 4th int class spells, 36 spells, 3 slots of 12/int, 3 BAB, light armors, assassin/streetwise/search/lockpick/stealth/pickpocket/forge/disguise)
Bard (warrior/spellcaster, 10 HD, 2 saves, 9 bonus feats + 4 weapons, 13 class feats, 5 special abilities, 7 cha class spells, level/cha/int slots, 4 BAB, light armors and light/heavy shields, streetwise/charm/sing/instruments/legends)
Wizard (spellcaster, 6 HD, 4 bonus feats + crossbow weapons, 37 class feats + 5 of 25 or 3, 3 special abilities, 9th int wizard spells, 41/int spells of 214, 4 slots of 36/int, arcana)
Psionicist (spellcaster, 6 HD, 5 bonus feats, 33 class feats, 9th int class powers, 41/int powers of 103, 343/int PP, psionics)
Druid (spellcaster, 8 HD, 2 saves, 1 bonus feats + light weapons, 13 class feats, 2 special abilities, 9th wis druid spells, 41/wis spells of 97, 5 or 4 slots of 41/wis, 3 BAB, leather/hide armors and light shields, nature/healing/animals/stones)
Cleric (spellcaster, 8 HD, 2 saves, mace weapons, 7 class feats, 1 special abilities + 2 domains, 9th wis cleric spells, 41/wis spells of 125, 5 or 4 slots of 41/wis, 3 BAB, all armors and light shields, healing/religion)
Bishop (Cleric, 8 HD, 2 saves, 4 bonus feats + mace weapons, 6 class feats, 1 special abilities + 6 domains, 7th wis cleric spells, 41/wis spells of 125, 5 or 4 slots of 33/wis, 3 BAB, all armors and light shields, religion)
Sorcerer (Wizard/Cleric, 6 HD, 21 class feats, 1 special abilities, 9th int wizard spells, 9th wis cleric spells, 82/cha spells of 214 + 125, 6 or 5 or 4 or 3 or 2 slots of 40/cha, arcana)
Psychic Healer (Cleric/Psionicist, 6 HD, 14 class feats, 9th wis cleric spells, 41/cha spells of 125, 4 or 3 or 2 slots of 31/cha, 9th int class powers, 41/cha powers of 103, 172/cha PP, healing)
Warlock (Wizard/Psionicist, 6 HD, 29 class feats, 9th int wizard spells, 41/cha spells of 214, 4 or 3 or 2 slots of 31/cha, 9th wis class powers, 41/cha powers of 103, 172/cha PP, psionics)