Whatever-class-you -are-most-comfy-with FTW!

Having played a warrior tank from MC back in vanilla WoW to T5 instances and now playing a tankadin in T6 instances, I think I am qualified to chime in here.
Armory links: Ivl Warrior Stephanius Paladin

For single character play in raids or 5mans it does not really matter what class your tank is. There are encounters where the one or other class has an advantage, but any discussion which class universally is 'the best' is utterly pointless.

Any competent warrior can multi-target tank, but there are limits to the amount of mobs and the threat maintained per mob. In a multi-mob pull, the warrior has to rely on DPS going for the kill target so that minimum threat on the remaining mobs is sufficient because only healing threat needs to be overcome. A warrior also has more options to use in most situations. The big problem is using the right one in the right moment and not fumbling with your buttons.

A tankadin's threat output is mostly reflective. Upon getting initial aggro, there is no per-target maintainance of threat needed. This scales indefinitely. It does not matter if it's 4 mobs or 40, besides the damage input. This is highly relevant when you want to AoE nuke groups. When using my paladin tank in multiboxing, I usually case two salvos to drop the priority kill target and then nuke the rest down using my warlocks seed of corruption. I usually use two warlocks and one mage as dps, which makes this work quite nicely. Nuking their heart's out, the warlocks do not draw aggro. Ever.

The great thing about the reflective threat on unlimited amounts of targets is that it requires only an intelligent pull and then relatively low maintainance compared with the frantic target switching and button mashing of the warrior. This is rather a question of what you prefer when playing solo, but when multiboxing and playing the whole holy trinity yourself, any cut-down in actions per minute is extremely helpful.