I use both, but tend to promote the Vimeo link over the Youtube one just because I prefer the cleaner layout. Some people seem to have playback issues with Vimeo on slower machines though so I think it's worth having both. Also the option to run a promoted video campaign on YT can be a good way to build your viewership, since Vimeo doesn't have anything like that you'd have to combine it with google adwords or something which probably wouldn't be as effective.