I am no expert by a long way but I was using Mach3 and recently rebuilt my setup and moved to UUCNC with an AXBB-E motion controller and loving it. Apart from an issue setting up the Ethernet comms it has been very good. If I knew then what I know now I would have moved to the AXBB a lot sooner. A couple of things that spring to mind where it beats Mach3 is that it has loads of inbuilt probing routines and starting from mid-program is instantaneous whereas Mach3 takes forever.