That's one of my reasons for giving my vote to
BA - I get soooooo cross with Virgin when they confirm your pre-requested seats but then don't deliver them

Also, I find the BA seats (economy) slightly more comfortable than Virgin's.
I dont think that problem is specific to Virgin - we have had that problem with BA twice before and our friends also had this problem. They were a party of 3 so easy enought to seat together you would think....but BA sat 2 near the front of the plane and 1 near the back of the plane?!
My vote definately goes to virgin for 1 reason - their customer service. For the last 3 summers they have had endless problems and did not deal with them or the affected customers in a very good way. Some people ended up with a 5hours+delay on the flight to orlando and no hot food on the plane this year! Not ideal!