i own an ez4lite (oldmodel) and a m3lite/m3perfectSD. Well ill just say this its not just about when your cart is in your ds and are playing. its alot to me about the UI and software. dont get me wrong compat. is important but its allready been stated ez4 has equal if not just a lil less compat. to SC and M3 for NDS and ez4>all for GBA well ez3still beats it but other newer carts.
I dont even use my m3's my gf uses the SD and i havent even really used my m3lite. Mainly i like my ez4 more cause of the tuchscreen UI, and easy loading of the microSD. Its just open game in software, name it if the rom naming isnt uptodate(fans update this list b4 ezteam normaly) and click send thats it! creates the sav for you and every thing its alot more steps to get newer games to run on a m3 you have to choose differnt options to make the game run and this usualy takes a few times in and out of your cart/sd reader.
I have noticed batt life seems to be abit longer on the ez4 as well. though im comparing the m3perfectSD to the ez4lite so i donno.
One down side for ez4 that used to take place was updates to the client/loader dont come as fast as m3's. but that kinda says somthing in it self. most new games have played first load on my ez4 and not my m3 having to resend it usen a safemode option in their client. or having to wait for them to release an update to be able to play it.
so as you can see im kinda a ez4fanboy these days, o did i mention my ez4deluxe is in the mail now. so ill be able to let my gf use my old one muaha good bye m3(till my ez4 dosent play somthing it does)
Edit- i noticed the comment title of this poll "Which is better for emulation (DS, GBA, SNES, NES) and homebrew?" With the exeption of homebrew its Ez4lite hands down all snes and nes emus run on it just as well as sc,m3 and like i said above ez3/4 are the best carts for gba.