Tanked as a druid and a pally through TBC. Switched to warrior in Wrath and have never once looked back.
Pally rotation is very static, and honestly doesn't seem fun for me at all. Warriors have sword + board, which makes their rotation variable.
Druid rotation is also rather static. I also got pretty bored of looking up a bear butt all the time. Even with the recent model updates for druids its still pretty boring seeing a bear. I like seeing cool looking armor on my character as I tank.
Warriors are also the most mobile of the classes. Three different charges, all on short cooldowns (although realistically speaking you'll probably never use intercept while tanking).
I also like that warriors are the best debuffers of a boss. They can put sunder up, which is class specific, and few DPS warriors seem to take the time to do it (even though its a big raid DPS increase), they can put up -20% attack speed, and they can reduce the boss attack power (which is a pretty big deal, mob AP is calculated differently than player AP).
However, I do miss my druids ability to shift out and huck a battle rez + innervate during phase shifts and such.