A warrior would be ludicrous and pointless - I have like five of them at 90 at this point. Even I'm not crazy enough to waste it on one of them. Right now I'm kind of stuck between mage, hunter and warlock -- all three are fairly different from my usual classes. I have a hunter at level 62, while my mage and warlock are significantly lower level (my mage is level 14, my warlock level 12) but I'm not all that concerned about deciding on a profession for them. What I really want is to use it on a class I might enjoy at endgame, but which the leveling style isn't for me, and which I haven't already played much - so I'm basically looking at the cloth classes.
Are you in the same boat? Did you blow your 90 boost immediately or do you still wonder what to use it on?