I do quite a bit of travelling and love flying in Upper class (but don't like paying full whack) so I use air miles credit cards. I've had the Virgin one for maybe 15 years and flown upper at least 10 times and all through using the miles gained on the spend. Normally used going to Vegas, Miami or Orlando. Virgin is probably the best one for the U.S.A or Caribbean. I always pay for the card which is £140 I think as you get double the air miles. I use it for my business as well which really boosts it up. That said the cost of a flight has risen. I flew last year to Vegas for 100,000 miles and I'm going this June and it was 160,000. Since they change the credit card rules (about not being able to charge you) the perks have reduced.
I've just applied for the BA Amex card as going forward I'm more likely to travel to the Far East and Australia and am sure that card will benefit me more, so I may switch to the free Virgin one. It's worth checking out 'headforpoints' to see what they say about the card. Also 'seatspy' for looking at availability of air miles with Virgin and BA. Loads of people say that they struggle to use air miles and so its a waste of time - I've used mine every year without a problem, you just need to look at how to use them best.