Wincnc is customizeable.
You can create your own screen, custom macro buttons on the screen, etc.. I found a thread a long time ago about that on the cnczone I think.
Price, well I agree Mach3 software is cheaper.
I have a lathe that I use Mach3 on, I love it but there is some kind of quirk where sometimes it will just freeze the computer. The only way out is to press the power button on the pc. I have a custom Lathe screen I created and I thought it was that but, it has happened using the regular lathe screen as well. I even tried a different computer and it happened on that as well. Yes I own a license so it's not an un-licensed copy.
In the 5+ years I have had wincnc, I have MAYBE once had it mess up on me. I have had Wincnc, Bobcad, Solidworks all running on the same pc at the same time, Running a job while Drawing a part in solidworks, then generating G-code with bobcad all while the job kept running in the background.
Not trying to bash Mach3, I really like it, the features, the support forum, i just have trouble with my lathe.
If I could have that kind of reliability in Mach3 I wouldn't hesitate to convert my Hardinge Superslant over to Mach3, probably even my (2) VMC'S too.