They are both the same, i'd say get the M3 as they have a good track record with keeping their devices up to date. But if you can't get M3's from anywhere just get the R4. You can always 'transform' and R4 into an M3 if you wanted, check the bottom of my M3 DS Simply guide. (link in sig)
Go with the M3, they're a company who has been around and offers good support to their products. The DS Simply is out of stock at most place but its only a matter of time before you'll get your hand son one. Its like the nightmare my wife and I went through trying to buy our Nintendo Wii a few weeks before Christmas. Although it was sheer luck for us, especially since we didn't have to wait in line for days like all the fanboys.
They are exactly the same hardware with only a solder link different. Chnge the solder link and you have the other cart. The R4 is slightly cheaper and the software is more developed. If at a later stage you find the M3 simply software is better, just change the link.
