I know we pretty much ask this in introductions, but let's make an official poll out of it! Feel free to post a reply elaborating, if you wish!
Oh, wow. This really is a tough one. I don't think I can choose. >.>
Mages and warlocks, describing the spells is far more fun than fighting with swords, although i like most classes for RP.
Warriors, and the reason for is explained in the guide I put together. They can wear and wield anything and they have the diversity to play any avatar I'd need. Recently, I've traded the bluntness of the warrior for the subtlety of Rogues or the eccentricity of Mages, but I'm a Warrior guy y'kno?
DeeKays can boil in a pit, though.
Warlocks and Rogues, Warlocks spells are very fun to describe. Rogues are quick on there feet.
Druids, because they're druids. . . I mean, come on, druids!
Definitely Mages and Death Knights, cuz I'm a sucker for magic 8D It makes a lot of things possible, and if you're creative enough, it'll lead to... interesting material... >.<
For RP, my favourite classes are Mage and Warrior. They are just the classic fantasy characters and I have more ideas what they should be like. I am unhappy to tell you that my favourite PvP class (Hunter) is a class that I don't enjoy RPing much... :?
Warriors!
They are the bread and butter of Warcraft. They are WARriors after all. They can also be used for many roles not just soldiers but as normal people, leaders, marshals, mercenaries and many other things.
This is hard to decide. But i reckon druids and hunters. Mainly because of their close ties with nature is great for RP.
Paladin! Faith is my armor! HATE IS MY WEAPON! Zeal, courage, strength of will more then strength of arm. Anything is possible with your faith in the light. My faith has not heart to piece, no mind to break, no will to shatter, not fear, my faith is unstoppable.
DRUIDS DRUIDS DRUIDS. D:
Also Warlocks. I really like what you can do with those guys.
Warriors. Not only because I'm in love with the raw close-combat, but also because they are versatile as to what roles they can pull off.
For me, my choices would be between rogues and hunters. Rogues have the ability to sneak around without being noticed easily while hunters can tame and nurture wild beasts.