My ideal panel would include a bracket for the Garmin 196/296/496 series. The bracket itself is relatively inexpensive and allows everybody to slip in his/her own GPS, with the flight plan, updates and everything already loaded.
Plus the pilots will probably be very familiar with their own GPS and not necessarily the GPS you choose for them. I have once seen a Diamond fitted with dual Garmin 430s take off with two additional GPSs (296s) on the dash, because the pilots were not familiar with the 430 and didn't know how to load their plan in them.
For serious aerobatics, just leave the GPS at home if you're worried about it coming out of the bracket during a flick roll or so. Saves a little weight too.
While you're at it, consider the need/wish for an ELT as well.