Death Knight, all the way.
Rogues are so underated in WOTLK for he reason that, No one ever sees a good rogue, so they dont want to invite one, people think class sucks, wich is as far from the truth as you can get, the top dps is bis combat rogue that knows how to play, sadly you never get to se them since they are more rare then skilled feral druids, wich also top dmg done easey, I belive this is due to that Feral - Combat rogue / enh shamans are the hardest classes to master in WOTLK.
So getting a spot as rogue in raids is just annoying as hell, people even say "you dont bring any good buffs" when you have savage combat that increases everyonce physical damage by 4%, it just shows how little people know about this class in general.
So I would really suggest goin DK It's a very fun class with alot of utility, you can play around alot with your talents and tank as Blood, Unholy and Frost since most of the DK's tank abilities comes from the gear and presence, the talents themselfs isnt as "boosted" for tanks like most other tank classes (except Druid wich is also more about bear form), the frost tree atm is very boosted dmg wise and when the new core gets implented Blood and Unholy will finally get to show their true colour.
DK's are also also allways welcomed with open arms to raids.
PS: My 2 favorite classes of all 10 is Death knight and Warlock.