This time Pathfinder only. Last time I was making it 3.P, but not everyone is playing with 3.X materials, so...
Tier 1: Cleric, Druid, Witch, Wizard, Oracle (with Paragon Surge), Sorcerer (with Paragon Surge);
Tier 2: Psion, Oracle, Sorcerer, Summoner, Bard (Magician w/ Paragon Surge);
Tier 3: Alchemist, Bard, Inquisitor, Magus, Psychic Warrior, Wilder;
Tier 4: Barbarian, Fighter, Gunslinger, Ninja, Paladin, Ranger, Rogue, Soulknife;
Tier 5: Cavalier, Expert, Monk, Samurai;
Tier 6: Aristocrat, Commoner, Warrior;
Now some questions:
Assuming that those placements are somewhat correct, what would each of the tier 4 classes need to become tier 3?
Barbarian is already a decent combatant, so does it need more and better skills or something else?
Ranger has skills, but his combat capabilities aren't that great without optimization, I think. Would something like Fighter bonus feat progression improve him?
Gunslinger I don't know very good.
Ninja is a variant of rogue, so maybe it is already low tier 3 like him?
Paladin... would adding Marshals (from 3.5) class features help?
Soulknife I'm not enough familiar with.