It took me some time, but I decided to simply proceed by elimination:
-Very strong and competitive in pvp early on
-Fun to play in pve, with a competitive dps
-I don't want to tank, I don't want to heal -Hard to get bored with
It means no paladins (ret is good in ICC, and in pvp holy is better, so I'd have to play holy and prot probably), no priests (shadow is real good but hard to play in pvp, and in pve it's just ok but nothing incredible, and otherwise I don't want to heal), no mage (I find arcane very boring in pve, and fire takes a lot of crit to get good, plus it's not my cup of tea), no rogue (assa is boring to me, combat too, and sub rogue is actually really hard to play in pvp in wotlk), no hunter (same, very tough to play in pvp to get WotLK Gold, and in pve I only like survival, which marksmanship trumps later on).
So, what's left:
-affliction and destruction warlock (destro not so much in pve)
-druid (feral, both in pve and pvp)
-unholy dk (both for pve and pvp), frost dk (for pve)
-elemental shaman (for pvp) and spellhancement/enhancement shaman (in PvE)
-warrior (arms for pvp, fury for pve)
So I decided to go unholy DK for pvp and PvE until Trial of the crusader, then I'll switch to warrior when it becomes viable.
So here's how I did it, care to tell me how you guys made your choice?