It depends on what you are looking for. The Q Acoustics have a smoother, fuller sound with plenty of bass weight. They really are excellent for the money. The BR5s sound more agile to me, though don't quite have the sonic authority. Details levels are pretty close. Both are good buys.
Thanks Ketan, my NAD is aleady a bass-heavy amp...so, maybe I must avoid QA 2050? I need floorstander that give more punch at the mid-high and treble...because, NAD+Marantz are very good in vocal and bass....Do you have another alternatives: maybe Mission MX 5?
Personally with that set up I'd take a look at the Monitor Audio BX5's; even 2nd hand/ex-demo they come in very good prices and they're better than the Q's or BR5's
In saying that you could also consider the QUAD 21L2's or 22L2's and even some 2nd hand Monitor Audio RS6's. Again these 2nd hand come in at great prices on eBay and other hifi forums and they'll walk all over the above mentioned speakers!
If you have the room for them, as they are a big speaker, I' d be more inclined to look at 2050i. Apparently very accomplished performers for the price and displaying no shortage of finesse to go with the dynamics. That'd be where my £500 would go.