The M3 has the best compatibilty of all Slot-2 devices (i can't comment on Slot-1 devices as i never researched them)
Here is a list of all games and which work and don't work, I believe there is about 5 games that don't work (which out of about 700 isn't bad) http://m3wiki.com/index.php?title=M3_NDS_roms
Game freezing or slowdown of streamed games is almost always related to people buying SD/CF cards which are not fast enough, I have a fast 1GB Sandisk Ultra II card and have never had any freezing or slowdown problems, but if i use a crappy unbranded 128MB card I have lying around games such as Tony Hawks and Spyro slow down tons, and games such as New Super Mario Bros just crash randomly when going thorugh doors/entering new areas.
Quick look at the list shows 18 games with problems and only 2 games that don't work, considering theres 756 Games i'd say thats very good compatibilty.
Just as a side note anyone know where to find a similar list for the Supercard/EV Flash etc. ?
