Not all support cards over 2GB,so forget the R4,old and no longer supported as far as I know.
M3Real is still OK for the price I believe.But if want the best and are prepared to spend a little more Id recommend the cycloDS Evolution.
Im running a 8GB MicroSD SDHC through the cyclo just fine.No rom patching neccessary,just drag/drop and play.
Home page of the cyclo and info on it here:
http://www.cyclopsds.com/cgi-bin/cyc...clodsevolution
Cant speak for the Edge and others but here some of those as good too.
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