What's the most compressed video file type? AVI? DivX? WMV? MP4? ect.?

[haxingninja]

and for sandis sansa users:
does the sandisk sansa media converter expand the video file?

 

[larsathin]

All I can say is that AVI is the least compressed file.
The rest are pretty well compressed, but I think DivX might be the most compressed.