Your choice of MCU depends a lot on the kind of projects you're going to be working on. Are you making high-volume, super-cheap and simple devices like flashing bike lights? Are you developing complex prototype robots which have to deal with numerous bizarre IO devices and sensors?
I mostly work on the latter. The main problem for me is trying to find microcontrollers which have the peripheral set I want. This is very difficult as our requirements don't seem to be mainstream. We want things like 5 PWM channels, 5 Quadrature decoders, 2 non-standard SPI ports and a UART with negated IO.
The only MCUs I have seen which can handle those kind of requirements with ease are the PSoC and the Propeller.
The Propeller is basically eight 32-bit MCUs in a single chip. If you want some type of peripheral, you simply program one of the MCUs to perform that job. So you can have whatever you want.
The PSoCs come on two flavours, 3 and 5. The 3 is an 8051 core, and the 5 is an ARM cortex M3. Also included on the chip are re-configurable digital and analogue blocks which can be made into a wide range of peripherals: ADCs, filters, op-amps, DACs, SPI, UART, quadrature decoder, CRC generator, etc.
The development environment is fantastic. You have the usual source code editing of a typical IDE, but you also have a schematic editor. You can literally wire up any digital circuit you like, connecting up the peripherals with gates, flipflops, etc. Need 5 PWMs? Easy, just put them into the schematic, wire them up, and away you go. You can even write your own peripherals in Verilog if you want something that's not provided. A great deal of your application can simply be implemented in this sort of hardware.
The real benefit is that you can stick with one chip, knowing that it can tackle a great many of the projects you'll want to do in the future. What I found annoying about PICs was constantly trawling through dozens of devices looking for the one which had the particular peripheral set I needed. Now I don't have that problem.