Ever noticed fuzzy, pixelated images, faded colors and other issues with youtube hosted videos? I understand you can improve things by carefully configuring your video for youtube parameters before uploading.
On the other hand, I usually have sharper resolution and better color fidelity using vimeo.com. Part of the process at vimeo is handled manually which seems to help.
You can compare the same video on both sites simultaneously to help comparison at:
http://fksa.org/showthread.php?t=4402