I'm slowly discovering that some of the best systems to mine are the ones with less than 10 belts, sometimes as low as one. It seems that people avoid these systems because there aren't enough belts, they probably think that it will be to crowded.
For this kind of mining the best location is one where the systems form a loop. I will mine in one system usually no more than two belts then move on to a new system the next day. At some point I'll go through all the systems in the "loop".
A good example is Gergish (Ombey 2d Map coordinates D7) in the Genesis region. Gergish is the beginning of the loop. Btw I've never mined that area so I have no idea how good it is.