Both systems are good...
They both require training to program.
If you are looking for an all in one solution then Crestron may be the way to look.
But
If you have clients that may want just a little lighting control, or other things without the full automation package, going the AMX route and becomming a dealer for the other things may give you more choices and solutions for your clients.

Maybe Lutron/Vantage etc have too many dealers in your area and are not looking to open up any more, Crestron gets you into lighting control.

Maybe there are too many Crestron dealers in your area, then AMX might be your best bet.

These are things only you can answer.

Being a dealer of either one means that at one point every couple of years you will be cheering because you now have the latest "whatever" before the other guys. Then 6 months to a year later your going damn, the other company has the best "whatever". Either way, both systems are there to control things and they both do well.