Hmm, let's see. A fighter 12 gets Weapon Specialization, Greater Weapon Focus, and Greater Weapon Specialization. It's hard to beat that. Who cares if you have actual "paladin" levels. You can still be a holy warrior. Or perhaps fighter 6/cavalier 6.
A barbarian 12 gets greater rage and 4 rages per day. Not too shabby. Plus you'd be bullish on hit points and thus hard to kill. You could even get decent AC with mithral full plate, although I'd say to focus more money on the weapon.
A ranger 12 gets evasion, 3rd-level spells, 3 favored enemies, and 3 combat style feats. Very impressive options there. Light on AC but evasion and good saves help make up for that. Plus you have an animal companion to grant flanks and occasionally do some damage or help track.
A paladin 12 gets 3 smite evil per day, 3rd-level spells, 3 remove disease per week, immunity to fear and disease, ability to turn (and choose divine feats), burst healing from lay on hands, and good saving throws all around on top of an intelligent mount you can summon when you need it.
I really don't see how any of the multiclass builds you've presented are superior to any of these options. Perhaps a fighter 2/paladin 10 for some extra fighting feats. Give up 1 remove disease per week and 3rd level spells for two bonus combat feats. Ranger 2/paladin 10 would let you pick a favored enemy and get Two-Weapon Fighting without having to worry about putting points in Dex. A barbarian 11/fighter 1 would still get greater rage but get a bonus combat feat in exchange for one rage per day. I think these are more realistic multiclass options to look into.
