I have used AusCAD which was what it was called before OneCNC. In fairness to it, I didn't use it much, but I really prefer Excalibur to it. I'm in Brisbane Australia(so is OneCNC by the way to the best of my knowledge) and I find it easier to speak with Don and get help from him than I would normally recieve from someone right here in Brissy.
Personally I believe this to be the biggest factor for Excalibur.
Aside from that, the post processor is very easy to configure to suit your particular machine.
I honestly believe you would be very happy with Excalibur if you decided on it over another package.
So in answer to your question, Technical support is excellent.....Even across the other side of the world, very easy to talk to and actually wants to help you with your concern.
I also find it user friendly, but I guess it is what you become used to.
I hope this helps..........Greig