Well its pretty simple if you have to choose between a human and a dwarf. Get the human! Now about the class:
DK if you are in for having one of the high populated classes, nice for AoE tanking but never expect to be a maintank if you have a good geared and skilled warrior besides you. But be ready to take some nerfs in 3.2 tough. Further on, you are wanted for HM's since your class is still overpowered now.
Warrior if you like to have a nice tanking char with a bit lack of aoe treath but being great as a single target treath builder and prob a main tank.
Paladin, Same as the Dk, Perfect to AoE tank on a pala, and with the 3.2 patch inc you will have a imba Last stand. Personally never exp a pala and never saw one main tanking so I cannot give any info about it.
you have never seen a paladin MT before?
My guilds MT is a pally and hes really well geared has 35k. unbuffed hp.
Im leaning towards a pally only b/c my GM told me if i decide to tank as a pally he will gear me up fast.
Any other comments/suggestions?
Further on, you are wanted for HM's since your class is still overpowered now.
What are HM's?
To OP, welcome to tanking, I'm new too and it makes WoW an entirely different, and more interesting and enjoyable game.
My best advice is to try to figure out which classes mechanics most appeal to you, and go with that one. Difficult to do that without leveling them to at least around 40, though. I have a 40 war, 40 druid, and 30 paladin (besides my old 70 Lock and Hunter mains), but never really enjoyed any. Check if any of your friends will let you play their tank in 5 mans for a bit, if possible.
Then DK's came out, cured my alt-itis, and settled it for me. I like the way they play - the rune/RP mechanic (don't like mana and rage), three different and interesting trees, each capable of tanking, dps'ing, or pvp'ing, and some interesting talents (perma pet, 20% mount speed for dailies, self-healing like my old warlock, etc.).
In fact, when I rolled DK I wasn't even thinking of tanking, but when I got to 80 and started wondering what next, it was either pvp, dps, or tanking, figured I'd done the other two, wanted to try something new, glad I did. Even if the choice of DK class relegates me to OT, as Faladir suggests, I have no problem with that. Fun either way.
It's also entirely possible that if you enjoy tanking, it may not even matter which class you choose, since it's the role that adds the most to the game, rather than the class.