5 sizes is way too much.

I'd stick to MOV and MPEG-1, the latter being the most compatible format that can play on any PC - windows, osx, linux etc.

The difference between MPEG-1, MPEG-2, MPEG-4 is in the encoding algorithym.

MPEG-1 being the oldest format hense more compatible with everyone, the files tend to be larger for the quality offered though.

MPEG-2 is what TV stations, DVDs and TV beamed down from a satellite use. HDTV is also MPEG-2 based, your digitical cable as well. Unless the user has DVD player don't offer them MPEG-2 encoded videos.

MPEG-4 is the latest and it differs in the encoding algorithym. Instead of looking at every frame, it looks for the objects that are in the frame. Any object that remains relatively the same gets re-used

DivX and XviD are MPEG-4 based, and so is Quicktime 6.5

The new standart is MPEG-4/AVC part10 which is even better than the previous MPEG-4 codec and will probably be used in broadcast media by next year. At least by DirecTV

So in short for best compatibility stick to MPEG-1. WMV for best size but it might not play everywhere