Once you've chosen your processor, you then need a board to put it on. If you create a generic board, you can move it to your next robot and use it as a development board. Depending on the processor, try using strip board, and try to get all the pins out on headers or screw connectors, this way its easy to expand without a lot of re-design. Also, try to think ahead, if you've got a series of pins that can be digital IO or an Analogue Converter, try using other pins first in case you want to use the converter later on. Also, try to keep similar pins the same between robots. It makes things a lot easier, e.g. PortA is xyz.