Druid.
Raided as every spec, though went from Kara to BT as Feral, stopped raiding, and picked it up months later as Balance. All in all, I still have to say Druid is my favorite overall class. I just ended up putting about 170 days /played with it, and needed something new. I wanted something that was difficult to master, and so far have been pretty impressed with the DK.
The rotations aren't to complicated, but you need to be aware of your Rune cooldowns, how many runes are used by your abilities, runic power, and pet if you're Unholy. As a balance druid, all I had to worry about for the most part, was refreshing Moonfire, and taking advantage of Eclipse procs.
Lots of fun. Currently DPS as Blood, and Tank as Frost. Gonna give Unholy PvP a try once I get some gear.