In terms of viewership, YouTube wins by far.
In terms of video quality, video edit capability, etc, there are many who win against YouTube.
For an immediate comparison of video quality on video-hosting sites, click this link:
http://www.lifegoggles.com/online_video_comparison.htmlYou can see YouTube's video quality is actually very low. However I think they are smart in doing that, because that improves the playability and speed.
Personally, I have used YouTube, it is my favourite for viewership and browsing.
Meat Pao.