I have been playing around with Aspect Ratio's (both on my regular pi setup and my Raspiboy) and tried a few out to see what looks best, as I felt the rendered image wasn't filling quite enough of the screen. I have now set my Raspiboy to use the 3:2 and I'm very happy with the results. Does anyone else use any particular settings that aren't the default ones? I just wondered what worked best for others.
FYI to change the aspect ratio globally, simply add the following line to configs-all-retroarch.cfg and restart emulationstation.