So G6 is out of the question. You've got 2 choices: EZflashIVlite or Supercard Lite.
I think cosmetically, both are the almost same. Supercard has cheap plastic and the split line between the 2 halves of the case and the little black hole for front loading is bad looking BUT flush. EzflashIV lite, cheap plastic, screw in the middle and not flush (but not noticible).
When I bought my EzflashIV lite, I thought the non-flush-ness will bother me but it hasn't. In fact, i didn't even notice it there compared to the 1.5cm stick out of M3 mini SD (which I preciously owned).
So now it comes to function:
if u want a library of 4000 GBA games and 500 NDS games, movies, mp3s (but lack of homebrew) go for EZflash lite [bad part is that 3 DS games have longer loading time, example: loading songs in ouendan, lag in castlevania intro, loading time in between buildings in animal crossing. BUT all gameplay is normal speed, just in between areas where there's loading]
If u want library of 500 NDS games, movies, mp3s, homebrew go for Supercard Lite [bad part is that some GBA games slow down (not sure what proportion)]
Since I have EZflash lite right now, I do feel that I'd like a supercard if I have the money so i can play the 3 games with no loading time, but i do not want to sacrafice the GBA games since there's quite a lot! Every GBA game I tested (old or just released) worked.
If you want the best of both worlds tho, wait for M3. Not sure if they will only have professional version (non-gba)... maybe they will have M3 micro SD perfect (gba + NDS) but it'll cost you big bucks.
When it comes down to price:
both are around the same.
Another thing to keep in mind (but superficial):
you can skin the EZflash NDS and GBA loader (both screens on DS loader can be skinned) whereas Supercard cannot be skinned and M3 can only skin on 1 screen (other is shut off).