If you are going to do this as a distributed systems problem, the controller does not need to be nearly as powerful, so this question becomes one of more preference than necessity. Either controller can, if broken down, easily control different segments of the robot you're describing.
This is the AVR programmer I own:http://www.adafruit.com/index.php?main_page=product_info&cPath=16&products_id=46
It's a build it yourself programmer that is really easy to use, and really nicely priced compared to other programmers. Programming AVR uCs really is not that difficult, and once learned can be invaluable throughout the rest of your roboticist days. This would also make your robot much cheaper, as "sampling" means free chips, and the chips themselves are ridiculously cheap anyway.
If you're interfacing with a laptop, this can easily be done with the same programmer, as it acts as a USB -> I2C interface as well (with some clever programming).
If you're looking to WIRELESSLY interface with a laptop, then that is different but still not a hard task. There are many RF forms of communication. I've recently began experimenting with bluetooth and found sparkfun's bluetooth to serial dip module:http://www.sparkfun.com/commerce/product_info.php?products_id=8461
to be quite easy to use and interface with. It's a dumb pass through - no authentication or encryption, just byte in, byte out. This should interface nicely with the AVRs, Arduino, or Axon.
Keep us posted on your progress!