Warrior. It's just kind of the best in every sense- enough to make a lot of people mad about it- but it does require some intelligence and maintenance. You'll have to do some homework to be good at it.

PAL is not quite as versatile but is a great set-it-and-forget-it tank. Very safe.

DRK... well, a lot of people are not quite really that happy about the way DRK is panning out. Not broken or anything, just has a lot of abilities that don't really play nice with each other and lacks overall cohesion. Some people say DRK is perfect! ... Some people said 2.0 War was perfect and everyone who complained was a filthy casual... Take a massive grain of salt with anything you hear about DRK, these are tumultuous times for it.

In the end, a Warrior is your best choice most likely. Fun, lots of potential, doesn't suffer the godawful disability of leveling to 40 without a tanking stance like Paladin, and it's always got tools.