Most "universal" type of video file?

[R.L. Grigg]

What is the most "universal" type of video file? What could be viewed  
on almost any system, Mac or Windows, without requiring certain  
packages or codecs?

.wmv
.avi
.mov
.mpg
.asf
.mp4

I have some .3g2 files to convert and have all these choices but don't  
know which one would be the best to give out to people. I don't plan  
to use any special encoding I just want to make a simple movie file  
anyone can play.

Russ