I did have some difficulty choosing between those two when I wanted to upgrade from my old 2PHKA. I ended up choosing the 3PM-FS (the synthesizing version) mainly because it has the programmable ABS (which the MX-3 doesn't). I haven't had a single glitch with it, but the menu navigation can be a bit annoying (you might "overshoot" the menu you want to adjust while trying to find it). Plus the 3PM has the optional HRS (high-speed response) mode, but only if you buy the corresponding R203HF receiver. I also like it because it's quite ergonomic and not that heavy. Both are good radios, but if you race nitro and need the ABS you have to get the 3PM. That's just my little opinion..I never used the MX-3 though.
TL-01, TB-02R, RS4 Pro 3, TA05R, Desert Truck.