Ok, Lament, many people tend to go for the R4/M3 Simply, but between those two I suggest the R4 because it get updates faster (you can use a tool to switch it to M3S firmware until an official comes out), and they are basically the same except for the logo.
Now, regarding PoR, you'll need a 1 GB KINGSTON MicroSD card otherwise it will freeze in that game. It's the fastest card available and the most recommended for the R4/M3S.
M3 is slot 2, and you can play GBA games if you get the Perfect edition, but it's more expensive (of course), but most people are into Slot-1s currently.
You can play GBA games if you wish by buying the EZFlash 3 in 1 Expansion Pak (Slot2). It's the cheapest Slot 2 available, and you need an R4/M3S or another other DLDI available slot 1 device to use the Tool needed to flash the games to the Expansion Pak (it does NOT take storage cards).
R4 + EZ Flash 3 in 1 + 1 GB Kingston at Dealextreme is 71 dollars. I bought from them, waiting for it to arrive.
Emulators work with the R4, so no worries.