Radials are better in general, based on the simple fact that it's easier to get a good feel, has to do with the leverage...

Then, what size you should have on the master vs the calipers, are more determined by BOTH numbers on the master and your preference... the diameter says nothing about the master really, what tells you something is diameter X throw, giving you the volume of fluid it pushes at what pressure on the hand...

Large diameter and short throw gives a rigid feel, good brake power but will make you tired in the hand, hard to dose... Small diameter and long throw, feels mushy and you need to really squese it to stop, but easier to dose... Somewhere in between you get a decent mix, where it feels solid enough, the volume your master is pushing is matching the calipers and the throw is long/short enough to get good feel... then you get good bite, and you can easily dose the amount of brake you use...