I can't answer your quesion as to the higher levels as my Barbarian warrior is only at lvl 32. I have had no trouble at all getting pick-up groups, LDoN groups, and contributing to guild raids up to this point. My HP and AC are decent enuf to make me an effective meatshield (especially with temp, but not always temped) and I can hold onto aggro in almost all groups.
The only exception was last night when I did a pickup group in the OT with some uber-twinked toons (one was a zerk) who were swinging a Sword of the Bloodsworn and Copper Hammer of Striking and hitting for 150-300 of non-melee. Most times I was able to taunt the mob back on me (taunt is in the mid 100s) but it was a little frustrating. (One guy flat out said that he had bought 50k plat to twink his character, and was planning on buying more, so what are you gonna do.)
This example is the exception, and I would not hesitate to make a warrior if you want a tank. I have been MT in every group I have been in with the War, except guild raids where a higher level warrior does the job. Downside to Barbarian is Barb is stunnable from front attack (as opposed to Ogre) and maybe not as strong as the 2 bigger classes, but I preferred slightly more well rounded stats. And, I don't have to be shrunk all the time. And I can smith Helanic Tundra armor eventually. Plus, aye git ta war a keelt!
My personal feeling is that if you want a tank, the warrior is the way to go. I should add that the zerker who kept getting aggro (although twinked) was severely beat up on the few occasions when I could not pull the mob off him. Guess he should spend his next 50k on AC/HP items.