I would have to say in my opinion that the M3 Real and the CycloDS are the best 2 cards on the market.
Both have good support. CycloDS has an active forum in English and M3 release updats and make improvements often enough /when required (RTS new feature release not so long ago).
M3 has 3 x RTS Slots for each NDS Game
CyloDS has 1 x RTS slot for each NDS Game
M3 Real has RTS for GBA
CycloDS does not has RTS for GBA
In Aus M3 Real $59 for an extra $20.50 (at time of purcahse otherwise $35) you get GBA Expansion Pak - Total $79.50
In Aus CycloDS $79 for an Extra $35 (at time of purchase or later on) you buy an EZ 3 in 1 for GBA Expansion - Total $114
M3 Real - Sakura nice, fast responsive menu, great movie playback, Old Sofwtare slow, unresponsive but still quite usable
CycloDS - Very responsive, quick and easy to use menu system
M3 Real - no in game light change
CycloDS - in game light change
M3 Real - no in game guide / txt reader
CycloDS - in game guide / text reader
There are pros and cons to both cards and there are other small differences too like you can auto boot into the last game played on the CycloDS but not on the M3 Real etc.
I have both cards and would no give either up for anything. CycloDS is my main NDS game card because it had RTS before M3 Real so my games are on that. M3 Real had inbuilt GBA support before CycloDS so my GBA games are on that - AND M3 Real has RTS for GBA games and I would never give that up.
The menu system is a matter of choice - I am still getting use to Sakura but at this moment I still much prefer the old menu system. Two reasons - I am use to it and it is not all that bad for me as I can spare the few extra seconds when I want to change game folders etc (although very annoying) and MAINLY the old menu system has 3 x RTS slots for each NDS game.
As far as I am concerned the M3 Real rivals the CycloDS on a NDS Game level but as far as I am concerned M3 Real blows CycloDS out of the water for GBA gaming.
Overall it is hard to say which is the BEST as it depends on exactly what you are looking for in a card. It all comes down to personal choice. Do you want 3 x RTS slot, or a faster GUI, background light changing or GBA support with RTS, is price a consideration / value for money etc etc etc. Once you can figure out what it is you definitely want and what you can live without then you can work out which card to purchase
I will add I would never have purchased the CycloDS if the M3 Real had RTS included for NDS Games before I bought the CycloDS - however I will NEVER get rid of my CycloDS and will ALWAYS keep my M3 Real too.
P.s. If anyone was to purchase from Aus I would highly recommend OzModChips with complete confidence and no hesitation what so ever.