Go with the M3 Simply or R4DS   There is absolutely no difference between the two except the sticker on the front   both are the same price, have the same menu and do the same things   don't let anyone tell you otherwise   just pick one out of a hat   They use micro-sd cards for storage and are the best in terms of performance - price ratio   after that i'd go for the M3 Real cos its the same but supports Micro SDHC   or if you want a NAND flash one go for the G6 Real which has 2GB Space and is a reasonable price unlike the DS-X whch is the same and has buggy firmware   Hope that helps...