We have done both routes with Virgin and i think it goes down to several considerations.
1 Distance to home from both Airports.
2.Flight cost (Im sure flights from Gatwick are slightly cheaper)
3.Hotel cost ( we use a hotel a Manchester airport that offers parking (15 days) and room for £89, Dont know about Gatwick hotels)
4.Will the later flight out of Orlando and into Gatwick give you more time or will you have to vacate your hotel/villa and have loads of time on your hands with nothing to do.

Just some considerations for you. The service with Virgin is the same on each route.