A well played Warrior can kill any Druid in PvP, and a well played Druid can kill any Warrior in PvP. Really, in my experience, it's a battle of speed and quick judgement (and of course gear).
Now, for tanking, Warrior are the clear winners, since they have *much* more aggro gaining abilities then bear mode druids. Plus, warriors they can take a much heavier beating. Not saying Druids are bad, just that warriors are simply better.
For solo play, Druids are better. They can kill things with cat mode, switch out and heal in a matter of seconds, and if things get hairy, turn to bear mode or travel form out. Warriors lack many "OH SH-" buttons other classes have, so we're stuck with health potions, one of our three linked 30 min CD's, or AoE fear. We know quickly when we're outclassed in a fight, and if running looks iffy, all we can really do hope we get some nice crits, or the mob misses a lot. Or, we can always curl up into a nice little ball and wait to be killed.
So, it's really a toss up IMO.
Edited, Sep 26th 2007 11:31am by Dradniless