Just to add my two bits to the discussion, I also favor the AVR series. A really useful HW platform can be nothing but a 2313 with a crystal (I use 9.216 MHz typically), a couple of 22pF caps for the crystal circuit, and a 10K, and 0.1uF cap for the reset circuit. The AVR can drive LED's (current sink) directly, and with the proper setup, I can make assemble, and reprogram the chip in less than 5 mins. after making code changes. BTW, the SP12 programmer (for the 2313) cost me less than $20, and that's including the ZIF socket, and small Radio Shack project box.
Jem