I haven't been pvping in wotlk for a loooooong time (retail wow), and right now, ret pallies are annoying as **** in lordaeron, although it should get better once everyone gets some gear at lvl 80. Still, I can't remember what are some hard counters to them?
Rets are awful for getting kited and killing healers. If you really want to put some hurt on some go roll a Mage, but at the same ilvl I find refs have a very difficult time against shadow priests and locks. Hunters can be good vs Rets as well if you time your cd's right. Unholy DK is good vs ret in a 1v1 fight, even with TE glyph gargoyle is OP. But Rets main weakness is getting kited, so I suggest a caster.
Frost Mages can have a chance against Ret paladins, but with no resilence, haste, mana and low spellpower they still can beat you by spamming cleanse and Hand of Freedom, Almost all classes need a bunch of stats to scale to level 80, But Paladins only need either STR or INT, so they are strong with gear or no gear.
Shadow Priests and Affliction Warlocks also perform very well against paladins, but that's at 80 due to being able to survive the initial burst with their defensive cooldowns plus resilence, have enough to kill them, make them bubble, wait for the balanced 12 seconds inmunity (Priests can Mass dispel tho, but It's really ****ing expensive), and then kill them again.
Either way, I would recommend avoid 1v1ing paladins this early. They have the upper hand with their dumbed down yet effective skillset. There's plenty of people leveling, go gank those ******ins