The both do everything you want. In fact, the hardware of both is almost identical. I think the real breaking point is the price, and R4 beats M3, I bought mine from Sky2k.com for under $40 after shipping (Chinese version by accident, I blame them), and a 1GB microSD is only about $10 more or $30 for 2GB. The R4 comes with a USB microSD adapter, a mini-CD with probably outdated shell software you can download from the R4 site, a rubber/plastic case for the card, and a wrist strap (who would use that?).
The R4 is working great for me, so I recommend it, but I can't say for sure which is the better of the two.
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