I haven't built a motor controller yet (I'm working on it, along with a BMS), but on other power projects I've worked on, the two contenders were usually Atmel and TI.
Atmel has very good development tools and is very straightforward to program. It also has a wide range of package/price/memory/IO options.
TI is much more complicated to program, but has some very advanced analog components (blazing fast A/D, and internal coprocessors that can take up some of the housekeeping). The C2000 series are in the upper range of price and larger package sizes.
I would look at Atmel first, and see if there's a good eval board that can get you started in experimenting.