Obviously he doesn't think the M3 Perfect is the best one. More than likely he's referring to some older NOR-based cards that aren't manufactured or sold anywhere anymore, like the Flash2Advance or X-rom or similar.
Personally I have a Flash2Advance Ultra and like it, though it's a pain to manually hex-edit the database to get PocketNES to use savestates correctly.
A lot of people seem to think that the EZ-Flash 3 was the best GBA flashcart ever. I've never had a chance to play with one, but it did look pretty neat. You may still be able to find one for sale somewhere, they're pretty expensive though.