[Iridium]

lightzout,

The only way to tell if your particular player supports both amv and mtv is to convert same file with both tools, upload to player, and test.

Tadad1 is abosolutely correct: Mtv not only does not compress files, it seems to add overhead of it's own, altho 30% overhead seems excessive. I would choose amv for files where quality is secondary to number of files. In fact I don't notice a huge difference in quality between MTV and AMV but AMV allows far more file storage, so AMV would be my first choice.
I.