Paladin.
Of the ones listed, definitely Paladin, though if you're not 100% sold on one of the above, Druid, Ranger or Animal domain Cleric or Inquisitor would be very useful, due to the action economy increase. Still, as I presume you're relatively sold on the above three choices, I'd have to agree with the Paladin suggestions.
If high level, Musket Master. Take Improved Snap Shot and Combat Reflexes. Use the level 11 signature deed on Bleeding Wound for free dex mod bleed upon a hit. Use a double-barrel musket with the Distance enchantment. Enjoy your 2*(1d12+bonus)+dex mod bleed to anyone who dares enter your 15-foot death bubble. Take Deft Shootist if you can or you'll suffer AoOs.
Don't waste too much moolah on AC--your best defense is gunning people down before they can do anything to you (and boosting your saves).
Consider a one level dip into Chevalier.
Look into special ammo for flexibility and consider keeping an extra musket or two in case something happens to your primary (store them in your Endless Bandolier).
Paladin for sure. Excellent saves, solid AC, swift action self-heal, and Smite Evil? Hell yes.
If you would be willing to go beyond what you listed, I'd look at Synthesist summoner, especially Half Elf. Take the Elf favored class bonus which reduces the time to summon your Eidolon by 1 round each time you take it, and at level 9 you go into Eidolon suit in 1 round.