Assuming both PE flights are the same price, I think you should stick with the airline where you have the highest status – especially if one gives you lounge access. But here are some thoughts:
BA WTP(PE) out of LHR serves the Club World meal but MCO is served by Gatwick and I’m not sure if that applies.
Virgin PE gives you fast track security at LGW whereas I don’t think that BA WTP does.
The Virgin upper deck used to be great for PE until they converted the rear section to economy. The effect is that when you land, there is a long wait to descend the stairs and so you lose the advantage of arriving at immigration before everyone else. There isn’t a curtain between PE and Economy.
If your flight is delayed by more than 3 hours, Virgin are much better at paying EU compensation.
Virgin (I think still) have the Disney check-in and bag drop – so you can deliver your bags and still make the most of your last day.