Wow , nobody has answered your question, or poll. I think it may be a problem with how you asked. I think that in a lot of gyros you would use all three meathods
Powder coat: on metal parts, such as the frame.
Auto paint on large area like the rudder, hs, pod, and any fiberglass parts.
Spray can: probably used on the inside of pods and areas not normally visible.
I hope this helps answer your question
Shawn