Youtube vs MyspaceVideo vs Vimeo Which is which?

Videos are amazingly informative and artistic. Nowadays video qualities have been improved and viewers are demanding for quality resolution.

High Definition (HD) videos are not only seen on HD TVs but also over the internet. I recently find out about youtube's "watch in high-quality" link...myspace's kinda high definition playback...but I just found out about vimeo, like youtube many people can upload videos, share, etc but the best thing about it is that it supports HD uploads and playback... So I'm a little confuse, which is which?