Mr. No-one said...
I like with youtube that you can skip to the end or anywhere in between without having to load the whole clip.
That's a big one I reckon, ****s me with vimeo. I think 'artsy' videographers just like vimeo because it's not 'main stream' in the way Youtube is and yeah they don't block music copyright atm.
End of the day I think they both provide the same quality, YT in 1080 looks just as good as vimeo imo; however youtube has way better servers a WAY higher viewing audience and if you use any other google products (gmail etc) it's all tied in so you don't need yet another account.