I've flown with Virgin a bunch of times and it has always been nice. I've flown with BA a few times and it has always been a bit uncomfortable, terrible food, grumpy service, dirty etc.
Watch out for 'code shares' though, some of the Virgin flights to the USA are actually run by Continental or United*, who are a bit like the Ryanair of long haul flying. I think BA may code share to some places also. You don't even get alcoholic drinks on them.
Having said all that, even though Virgin is much better in my experience, there's certainly not enough difference between them to make up for 25% difference in price. For that difference I'd probably fly Continental or United if I had to.
Joe
*I think London to San Francisco is sometimes a code share so do check this.