Top Ten reasons why I like the AVR:
My reasons reflect my earlier experiences with the Motorola 68HC11 and 68HC12.
Reason No. 10: Atmel continues to rapidly upgrade
the AVR lineup
Reason No. 9: Separate data and code model - less flexibility but fewer mysterious problems
Reason No. 8: I haven't fried one yet after 8 months
Reason No. 7: Atmel supports the little guy developer - good app notes and cheap development tools
Reason No. 6: Wide range of devices from 8 pin 1K to 128K that, with minor differences, all work basically the same way. Learn one and you pretty much know them all.
Reason No. 5: They're fast.
Reason No. 4: DIP packages
Reason No. 3: An operating uC with enough memory for a useful C program for under $10 - don't need to buy a board, just a chip and a couple of components (unless you want a 128 of course)
Reason No. 2: Excellent development tools, such as AVR Studio and GCC, for free.
Reason No. 1: Fewer "Duh - how can this possibly not work" sessions