DIVX or XVID

Wich one is better on the M6? DIVX or XVID ?

DIVX files are smaller then XVID files, so I use DIVX. But wich one is better on the M6?

Actually no one is really better than the other. Both should play fine on the M6, provided you do not use 'advanced' functions such ad B-frames, quarterpixels and stuff like that.

And as for the smaller files part, divx is not better either, they are roughly both as efficient, it will depend on the video I guess, and the bitrate/quality level you asked for. There is no general rule.

That said, my personal preference goes to xvid, just because it's open-source and divx is commercial... And i never had problems with it (not that I use the video functionality that much though).

Personally I find I get less problems and better quality using divx.

I noticed divx has better performance in the M6 than the xvid too.

what are all the codecs that the m6 can play?
Can it do .mpg?

No it cannot do MPG. It only plays Xvid and DivX .AVI files.