I have some experience with microchip PIC's. None with AVR's. As microchip will give you as many as 10 free samples every couple of months i went with them. The 18F452 chip is nice i have a few projects that work very well with them. They are being replaces with the 18f4455 series i think. You can make a very cheap and very easy to use multi programmer and debugger, its an ICD2 clone and the one i built didn't cost me much at all as all the chips were samples and I used some 3406 transistors and the rest I got outa my junk box. Microchip has another good series of chips that have built in usb support. Motor control. There is piles of them. AVR's have some excellent features as well. Almost all of the Univeristy level projects are using AVR's. Basically it came down to who would give me free samples over having to buy chips. Most of the samples i ordered from microchip arrived in 3 or 4 days, thats not saying much to some but in canada anything less then a week seems to be a miracle. Microchip has there c18 C code program that is an addon for the MPLAB IDE suite. It has a student level i think 2K lines, not sure on this i haven't written very large programs and haven't had it not work. I used the ccslite and it worked well for me. I tried playing around with the Renesas microcontroller but gave up after fighting the size of there chips, lqfn is not a very friendly size for hobbiest, 0.8mm trace seperation. Anyways hope this helps. Here are some of the sights i get most of my PIC info from.
http://stolz.de.be/
ICD2 clone, i built the rs232 version, took a couple of evenings works great. The USB one would be better to build from the start.
http://cstep.luberth.com/
Made a 18F452 controller to run his stepper drive's
http://www.mikroelektronika.co.yu/en...ok/picbook.htm
Books and other helpful info
http://www.edaboard.com/forums.html
Very good resource for anything electronic, as well has a very good forum for microcontrollers in general
http://www.winpicprog.co.uk/pic_tutorial.htm
Little outdated but a very good tutorial on pic programming.