So i've all but decided to use dsPICs for my next robot, and while googling online I found that these chips are surprisingly unpopular. I mean, compared to normal PICs or even AVRs, they are quite a bit more powerful (especially if you count the dsp stuff), they have a fairly good architecture compared to the pic16/pic18 family, and you can get a free compiler (gcc port, though less optimization for the free version).
The only thing I find that could hold people back is the programmer, but PICkit 2 isn't prohibitively expensive.