I play a Paladin, currently lvl 23, and I don't know if Paladin is the worse tank class in the game, the best, or somewhere in the middle, simply because I have never played the other tank classes.
I can say that the few times I have grouped with other tanks classes, I have never seen anything that would lead me to believe that they are worse or better. Some players played poorly some did very well, but nothing I saw suggested to me that one class was inferior or superior.
I can say that from play experience, my DPS is low, but my DPA is very high. I have not grouped with a large enough cross section of the Rogues out there, to properly establish a "norm" or baseline, but the Rogues I have grouped with, for whatever various reasons, could not match their cumulative DPS to my DPA over time. Many times against a named mob, they will even get "Immune...Immune...Immune," responses. So far, I am lucky to say, I have never gotten an "Immune" from an enemy. In fact, of all the groups and duos I have been in, the only class (same or near same level) that has been able to consistently out damage me, is the mage classes.
I can say that I have done well overall, holding aggro in groups. The few times I have had problems, was caused more by my poor decisions, than character ability. With all the new spell I have, many doing very well at generating aggro, it is easier than ever.
I can say that almost every single group I have ever been in, I was chosen as the main tank, over other tanks, including Warriors, Guardians, and Monks. The primary reason, was because my mitigation and avoidance, both were the highest. This wasn't because my class is better, but because I had on better armor. If players don't continue to upgrade their armor, it doesn't matter how good the class is in theory.
I am not qualifed to answer your original question, which tank is best at 30, because I am not at level 30 yet, and because I have not played the other tank classes to level 30 either. I think it is fair to say, that most people have not. Perhaps there is someone out there who has and can give us a more objective opinion.
Regardless, I have had a great experience playing a Paladin and the biggest lesson I have learned, is that THE most important factor in determining how good a character is, is how well YOU choose to play them. I personally think you will have fun and do well, with any class you pick. Good luck, and let us know what you decide to go with.
Edited, Fri Apr 8 18:06:46 2005 by Kallirye