Great post ceraphis!
I guess everything has been said about the two cards really, but I'll add my thoughts.
I have both the G6 Lite and M3 Lite and it's a tough tossup for me. The things I like better about the G6L than the M3L are:
Nice clean boot (the M3L flickers the screen just before it finally gets to the media menu)
The menu interface game icons are really nice (M3L is just all txt)
Boots straight to games menu (M3L starts at the media page and has a splash screen even before it gets there)
Touch interface (none on M3L's DSL media menu)
L/R triggers scroll games list (the do nothing on M3L, but you can page with left/right pad)
One button or touch to run game (M3L you have to confirm the save to be loaded first... Would be nice if save confirmation was an option)
Easily backup original cart save files (can't be done with M3L unless you use Rein a homebrew app)
The white DSL cartridge cover is a close match than the M3L's
The loading screen for when a ROM loads is nicer (M3L is two boxes loading boxes of txt)
The G6 uses both screen for the menu (M3L is just black on top)
G6 feels more compatable... I would just hit soft reset/trim/dofat and everything seemed to work... I have to be more careful with the M3 as to which options I use with each ROM)
Nicer packaging hehehe - nice tin and GBA cart included (M3L was just a box)
More cartridge covers... (navy blue).
Save management system
Things I like about the M3L better than the G6L:
THE SPACE! OMG I have a 2 GB micro sd in it and I just love how much I can get on the cart (G6 is 1/4 the space of that)
Loading on ROMS to the micro sd is way way faster than loading ROMS to the G6L
Cartridge cases feel much sturdier
Easier to firmware update... one file dragged to root of SD and then boot the M3L. (G6L is more complicated then that - not difficult, but takes more time)
Flashme is recoverable (G6L not)
THE SPACE!
Shows more ROMS per page (5 on M3L and 4 on G6L)
M3L sorts the ROMS on the SD alphabetically by name (G6L just shows them in the order they were written)
Overall, I like the G6L better, but I will be using the M3L because of the space (not gonna sell my G6L though)... If I had to choose just one, I would get the M3L, but only because of the micro SD slot - if the G6L was 1 GB or had a micro SD... I would be all over it!!!
The perfect cart for me would be a G6L with a micro SD slot and the menu tweaked to show 5 game icons at a time. I would jump on it!
Goodluck with your decision. I think anything you ever wanted to know about them is in this thread now
EDIT: Just added a couple gifs to show the "from boot to game screen on the two carts"
G6 Lite
M3 Lite