In terms of weight and size, probably the best computer to put on a robot (as a replacement to the rc ) is....
I guess that's off topic, since an apple machine can't run linux out of the box (it would have to be installed), but with a simple USB device (to handle the PWMs, Spikes, and inputs), it could be a reality. It would allow for a much greater degree of accuracy with autonomous, etc, would be about $800 (500 plus the cost of a USB device to link / contain PWMs and spikes), and would be very powerful (I think 1.3 Ghz is the slowest one they sell) to allow use of high-level programming languages.
If someone wanted to, they
could make a PC like that, but why would they?