I vote for TI's MSP430 series. I've used PICs extensively (also Atmel chips a little) and by far the most important thing to me is a good debugging IDE. TI has done a pretty good job on this, and their C++ compiler works really well. You can get going with an eval board for less than $100 including an IDE + USB-debugger. The PICs have better & more diverse hardware peripherals, but MPLAB is a piece of crap and the only C++ IDE for PICs is one by IAR which is rather expensive. (more than $2K)
