I really like the mp4 format. It compresses down nicely and the quality is very good. The only problem is that most people simply can't play this format as of today. I'm using a php gallery and it would not accept the mp4 files. Called it an invalid format.

Most of the time I use Imovie (mac) to convert dv to .mov files. Quicktime files are rather large with so-so quality. Not impressed with avi's at all. They take forever to convert. I really like .rm and .wmv for the best output with final cut pro.