What class is best for you depends on... you. It's different for everyone.
Are you a power gamer, or would you be fine with having fun as a class that is notably less powerful than other classes, as long as you enjoy it? Do you like to do one thing well, or prefer being able to fill a variety of roles? Also keep in mind your PvP ability doesn't cease to be a factor at 60, especially on a PvP server. Picking a paladin to avoid ganking is a short term reason.
One thing is not debatable however: the pure damage output classes (rogue, and to a lesser extent mage) have been gimped in the name of PvP balance. PvP is highly dependant on damage output, and to that end the spectrum between the classes on this ability has been greatly shortened, tanks and healers getting buffed constantly to do more damage, rogues getting nerfed endlessly to do less. It may make PvP more interesting, but there's no reason from the power-gamer standpoint in PvE to play a rogue when a warrior can do as much damage while wearing plate armor and retaining the ability to put on a shield and tank; no reason to play a mage when a warlock with twice your hitpoints and various utility such as banish, buffing, magic dispelling, etc. can do as much damage. Granted most people do some of both PvE and PvP, but (yes I'm a min-maxing powergamer) I want to be as good at each as possible.
Between paladin and priest I'd definitely go priest. makoto00 may have been right a year ago (I wasn't into PvP at all then - in fact, I wasn't even playing then, I had taken a break), but shadow priests are currently a nightmare in PvP. I'd put the PvP pecking order at warlock > shaman > shadow priest > the rest currently, with warriors in the mix, depending on their gear. The really well geared ones can slice up *anyone* - they're an extremely gear-dependant class. Keep in mind shadowform is a nice ability, but a shadow priest can still inflict a lot of pain without being in it - which allows them to easily shield, heal, etc. while kicking ass.
The real deciding factor, IMO, is the ability to heal. It's a meal ticket to PvE content - in a game populated mostly by 12 year olds, the damage output class population is very high, the healing class population very low. Healing just iz n0t k3wl, u no? Healing = variety to me, a break from the norm, since in PvP I'm an offensive shaman, healing only flag carriers in WSG, friends and mages when I need water At 425 passive lightning damage with a toep, my high crit has been a 3096 chain lightning. Let's see a rogue top that. And I can heal and wear mail / shield to boot. See what I'm saying? Same/more damage, but with the ability to heal... Blizzard's attempts to balance this out have been few and ineffectual. Giving the dps classes aggro reduction for PvE for instance, and more varied abilities for PvP. It looks good on paper but falls short in-game.
Anyway, definitely a priest, definitely not a pally. I'd also look into warlocks and shamans </bias>