With Dk's you do have a head start in that you'll be 58 so much quicker. (Excluding heirlooms and guild perks of course.)
Personally you have to think of the 'flavour' of the tank you want to play..I know this sounds stupid but how long to you want to stare at a character you don't really gel with? You can search forums and no doubt they will give you the ultimate Combo Class-race but if you can't stand gnomes why play one (or orcs/trolls/tauren/human etc..not wishing to bias against gnomes!!)
Easier to tank with is a moot point..you have tanks with shield, or tanks without. Think about a tank that has 3 different ways to mitigate damage, a tank that has 2 ways to mitigate damage and heal themselves passively or a tank that soaks damage that it can't dodge.
I've got all four and from a personal preference I find my warrior and pally easier to tank on. My Dk is still not a comfortable choice (and yes I love the idea of swinging a huge mace into someone's face but it just doesn't sit as comfortably as a dwarf with a tea tray on his arm!) As for my druid, well sadly she's not moved much as I've just lost interest in her and the druid tanking style (Please don't kill me Druid players!)
If this is your first foray into the world of tanking, which from your post I assume it is.. I would suggest warrior to get used to the threat mechanics and how you need to control the fight before looking at other classes and how they deal with things. Once you have the basics solid in your mind you will find the understanding spreading to other classes of tank and then all will become clearer.
Try all of them out on low levels, see how they "feel" and decicde what you like most. Sure, you will not see their real problems and stuff at low levels. But it's quite easy to get around lvl 20 and you can get at least an idea about their gameply by then. Somewhat higher would be even better. Well druids take longer to get to a point where it's ok to tank with them and not get frustrated. They just don't get an ability to hit multiply targets, early.
All tanks feel different. It's imporant that you start with one that you like to do. And that the rotine stuff is easy for you to do.
I think paladin is still easier than warrior as a first tank.
I mainly decided for the dk because of the blood shield, and the idea of healing myself, which gives me the chance of being a bit more independent in 5 man dungeons and also that I dont have to rely on the healer that much..
I guess I would prefer the Paladin as my first Tank then, because bubble and all that stuff must be usefull in certain situations, in case I pull to mutch. I personally only played a warrior till level 20 but it bored me kinda :/
You said u have got a druid tank, isnt that the best class at the moment, because your life is probably the highest, and so your able to at least take some crits?
If you like the idea of self healing i would agree with Katzazi and go Paladin - Seal of insight and Word of glory are perfect self heals as well as the Oh S... button of lay on hands.
No tank should suffer a crit now..as a druid back before Cata we could soak them up and not stress about the magical 540 def cap (leather with Def on was...well rocking horse manure springs to mind!) So back then we had a health ocean (like a pool only bigger...much bigger) to soak the crits and still walk away with that huge ol' bear butt swinging. Now all tank classes have a talent to make them uncrittable (Goodbye Def cap...was fun but ya know..the kids have gone to college now and Mastery's just so much hotter..)
Each class has a mitigation tactic these days, so if Warriors don't float your boat would definately advise Paladin.
However I would stress..you will not be independant in instances..The reason they are five man is that you will neither do the dps or self healing to solo these things (unless old ones for achievements/fun/profit.) I'm sure others will agree that you may be the guy in front taking the pummeling and, yes when you hit heroics, self healing will be used to keep you alive but without that one person using their talents to keep you taking that axe to the face you are going to fail..your group will wipe, and then there's all the finger pointing and blaming and it all gets unpleasant....
So don't do what so many other Wrath-baby tanks are doing and think you can solo stuff, talk to the others in your group, most importantly your healer to get feedback on your tanking ('was i squishy?' is a great one but don't ask your healer partner/gf/bf that...could get awkward! :S 'Maybe how was I to heal?' would be better...)
Communication is the key to a good tank, experience follows, and there are a great many people that have the time to help..You made the right start on these boards.
And finally...sorry long post, don't ever think you've stopped learning, I've played since first release and still check stuff on the boards.
All tanks are balanced against each other. DK (and paladin) don't get healing over the same survivability as other tanks. That's especially true for DKs. So you will not be more independent than other tanks in 5mans. However some soloing may be easier, but warriors have a self-heal there, too, as soon as they kill stuff. And they have stuns.
Bubble is nothing to use if you pull too much. You lose aggro when you use bubble. However paladins have a nice toolbox to save people and some good CDs. DKs are king of CDs at the moment. But they are balanced around using them. Warriors and DKs have nice tools and utilities, too. They are just different from those of a paladin.
About the druid: High amounts of life are not as important anymore as it was in Wrath. To be honest, before heroic raids, it's seldom valuable to increase it over what you already bring with your gear at least for block tanks (paladin, warriors). And no tank (at least at a relevant level) will take ANY crits. No tank did so at least since BC, because every tank geared against it. Now there is even a talent (that bears had in Wrath, already) so that they are crit-immune. (NPCs dont crit with their casts, so it was all about melee-crits.)
Anyway, as with DKs: Druids high health is balanced against other tanks having other options. They are not equal in every regard, and there may be some bosses where one is better than the other at special tasks. But they are so close that player ability makes a much biggere difference than the class itself.
So to be as good as possible you don't chose the class because it's better than others but because it fits you better than other classes.
for first tank i would definately advise pally to start with as they have alot of utility and oh shit buttons and are a bit more forgiving for when your learning how to tank. warrior is also a good choice for starters. dks and druids arent quite as forgiving. however, once u feel comfortable with tanking it all comes down to which class will you enjoy playing for an extended amount of time. so if your looking for a good one to start with to get you comfortable i would say pally, if your not too worried about that then pick whichever class you feel you would enjoy more
Okay first of all thank you soooo much for all the replies I guess I will then go for the Paladin. Now, there around a billion guides on the internet which praise to know how to tank. Like I kinda figuered it out, all of you have said that it comes with experience, but are some of you actually raiding as a pro Paladin in Cataclysm atm? And if I find a group shall I therefore tell them that I am new so they can kinda prepare for a loss of aggro or something, or would that cause any trouble of the people being "noob" and whatever?
You should start to tank as soon as posssible (thats lvl15). People at this level assume that you have only few abilities and are new to the character. They will not know if you have another tank or not, and they will probably not care.
If you keep doing dungeons while leveling and keep tanking in them you should be fine while you are doing so. When you reach higher level you at least know what to do whith this tank at this level more or less. If you get to higher levels and remember that your tank may have done something special there, and you cannot remember what this was exactly, just ask your group if they know about that encounter and tell them that you have not tanked this dungeon before. They should be fine with that, if you are doing ok as a tank.
Remeber nobody will assume that you are the perfect player of that class when you are leveling up a new char. Nobody is. They know that they are not perfect with their class (and maybe role) either. When you reach 80 you should try to tank every possible dungeon, too. So that you know them from the tank perspective at normal mode. When you reach 85 you "just" have to add the heroic stuff. Maybe you want to go with friends for the first heroic runs, but you will see how you feel when you get there.
Btw: It's a good idea to run with friends, while leveling, too. At best with an experience tank. A tank who has done the stuff herself will know the difficulties and know what you should be able to do and what not. That's probably the best advice you can get. (It does not have to be a paladin.)
ahh theres the problem :P My palading is already lvl 68 because I have been running dungeons as a heal. When you say playing with friends, I guess thats a good idea at the beginning because they might be a bit more forgving
What raid would you start with after being equipped with heroic gear?
And now, atm my pala is a b11. Would you suggest switching to a tauren because of the 5% increased stamina or should I just leave it as it is?
I said friends not only becaus the may be more forgiving. But if you can tank at least ok, only friends will try to push you as far as you can. Other players will either give you as much time as they think you need or will not care whatever you do. Only your friends will eventually start to push you some more, but not too much. Only they are interested to see how far they can go with you, until you just cannot take more, without going too far. It's one of the best ways to learn how to tank. If you allow them to do so, and play good enough that they trust you enough they will give you the chalenge you need to improve. And if you can do it, it's just great.
Have to say just stick with people you know and trust and you'll be fine...remember though you're not there to dps so make sure your first goal is survivability after that, build experience and understand...then when things are comfortable think about heroics and then raiding...Walk before you try to run!