The key difference between YouTube and Vimeo is that YouTube has an overabundance of content, as there are currently over half a billion videos on YouTube. Out of all the sites that support video content, it is most likely that you will find what you are searching for on YouTube.
Vimeo, on the other hand, only has about a million videos. They only allow up to 500MB while YouTube permits you to upload 20GB. There is no limit to the length of videos you can post on YouTube. However, there is a limit on size.
Vimeo will often display HD quality video but only up to 720p. YouTube, on the other hand, allows videos that exceed the maximum 1080 p resolution for TVs. YouTube videos can also be shown in 3D, but Vimeo does not have this feature. However, YouTube has a lot of cool features with which you can play.