Post by nihmue
Ok I'm a bit biased with my warlock main I love to bits so I would say 'Warloooock! Level the lock!11!', but it all really comes down to your personal preference.. level both a bit to see what you like best.
I can give you my viewpoints as an affliction lock:
PvP:
I am having a good time with my lock in there, the dotting on the run, teleporting and fearing is awesome, and you have a lot of health coming back from all your targets with spells and talents. Your felhunter will also provide you with nice silencing abilities and can get you out of fears, sheeping etc. You are squishy though, but so are mages. Sometimes I like to apply silly suicide fearbomb tactics just for the hell of it and run into a group of enemies dotting as much as I can and fearing with howl of terror. After which I die, but if I time it right I also see several of my enemies dropping dead after my own death :) Dropping an infernal in the middle of a slacking group of enemies is also fun (mind you these two examples are not the most useful things.. but I love doing it haha)
I have met some very, very nasty frost mages in PvP too though.
If you want to know more,
this is a very nice and entertaining read (bit outdated, but still very very good)
Leveling:
leveling as affliction is a breeze. You will have very good health and mana regenerating abilities, and you will have no downtime at all after a certain level. Running around dotting everything you see, mob after mob, coming out of the fight with more health and mana than when you started and then casually strolling back to loot the X corpses littered behind you... awesome :)
Affliction used to be THE leveling spec for warlocks, but now we have the LFD system, destro and demo can be pretty quick as well (I think destro would even be preferred if you will do loads of dungeons)
Consumables:
you won't have to drink or eat really as an affliction lock, you won't need to feed your pet and things like arrows are not needed either ofcourse. Only thing you need are soulshards, which will come naturally since if you do it right you will be frequently using the spell that creates them.
I have quite some alts, and my warlock is still by far my favorite. Insanely fun to play :)