Most of the important homebrews work on EZ4, e.g. MSN (BeUp) and a multimedia player (Moonshell).
Supercard Lite -> More flush, perfect DS speed / support with normal MicroSDs, homebrew support is better, hard to take out, butt ugly menu, GBA speed / support sucks, front loading MicroSD slot and cheaper I think
EZ4Lite Deluxe / Compact -> Less flush (not really noticable), average DS speed / support (but there's lots of potential and it's the second flash cart to support the new Star Wars game
), perfect GBA speed / support, beautiful skinnable and touch screen interface menu, homebrew support is average, MicroSD is still a bit hard to take out, really easy to take out of the DS, has a glossy layer and a bit more expensive. (unless you get the Deluxe, which has no GBA support).