We've done both and they each have their pros and cons.
Virgin has better seats, no doubt, especially when converted to the flat bed.
As others have said, the smaller cabin does make it nicer. Also, you can stay in the flat bed position for landing, lovely!
The BA seats are smaller, but they do have a divider that you can put up during the flight to have all the privacy you need. I had a backwards facing seat, no issues with that whatsoever. It is a slightly different feeling during take off and landing, I thought it was rather cool. So I really wouldn't worry about that.
But on Virgin the inflight entertainment is a let down. The Orlando route still doesn't have an on demand system, no pause or rewind. So on that one, BA wins.
Lounge: pre flight we've only had the Virgin Clubhouse before the refurb and I thought it was better than the BA one. Nothing wrong with the BA one, but the Virgin one had hot food and better drinks rather than the self service at BA.
On the way back, they both use the Delta lounge at MCO which is somewhat disappointing! Comfy seats and a drink, but no food to speak off.
Arriving back at Gatwick, it's full marks to BA with their arrivals lounge. Being able to take a shower and have a decent breakfast, is a world of difference. Virgin doesn't offer an arrivals lounge at Gatwick.
Food wise, although both were good, I preferred the BA food. That might have been just down to the menu when we flew. Also, BA doesn't have the awful Virgin Cola, so that's another plus for them.
Overall, in my opinion, they are both great. But until Virgin has upgraded the inflight entertainment on the Orlando route and gets an arrivals lounge at Gatwick, we'd probably choose BA over Virgin on that route. That said, we will be flying Virgin UC next year, one way but from Miami. That way we have the better inflight entertainment and an arrivals lounge.