After getting poor service at VS, I came here and was immediately helped by someone. And even if she hadn't of come by, I would have been OK because La Senza's store is much better organized, with a dedicated section for strapless bras (rather than the oh you just have to open all the drawers in your size to see if it comes in a strapless format and I'm too busy to help you out).
I've been to La Senza a few times this past year, and have always been helped by the staff. If you've never gotten a bra fitting, definitely take their offer for one. You might be surprised!