Thanks for reply.
So if I understand correctly APM is older technology, not developed as Pixhawk.
If I choose Pixhawk- what software do I need to control it?
A couple months ago I chose APM because I have some experience with Arduino and wanted to be able to hack this thing using 3DR's modified Arduino IDE.
However, 3.2 release candidates for the APM/Pixhawk firmware are out now, and the devs have had to remove some features in the ArduCopter version to fit it on board. I'm losing Terminal access and optical flow sensors, I believe. Pixhawk gets the new features in ArduCopter 3.2 without losing any of the existing features.
You're on fixed wing, so maybe things are a little different, but unless ArduPlane is much lighter than ArduCopter on the hardware requirements, go with the Pixhawk.
In both cases, you can use Mission Planner on Windows, or APM Planner on Mac and Linux. DroidPlanner 2 for Android is pretty good as well, but to get started you'll definitely want one of the two former programs, as I find them much better at keeping me informed as to what the copter is doing.
One option could be Gluonpilot V2.