I've currently got two BW saxes, a baritone and a curly sop, both in phosphor bronze. They are undoubtedly brilliant for the money, although their prices are creeping up now that the brand is getting established. I also have a couple of Yanagisawas, as well as some vintage stuff. Although the BWs are great, and well made, having owned both brands for a few years, I don't find them to be comparable to Yanaigasawa in terms of build quality. The Yanagisawas have better casting, have stronger keys (I bent one key on the BW sop just with finger pressure), more precise assembly and fit and a better finish. Peripheral stuff like cases and mouthpieces are far better on the Yani, too.
However, what you're looking at is a case of diminishing marginal returns. A Yanagisawa would cost two to three times the price of a BW, and if you apply a value judgement you would probably find the BW comes out on top. Setting aside price and just comparing like with like, though, there is no doubt at all from my experience that Yanagisawa saxes are higher quality than BW.
The point Jazzdoh makes about Mauriat pricing is interesting as well. I remember when they first hit the market here, when they were very aggressively priced. As soon as the brand got established their prices went to the same market levels as the Japanese and European opposition. I think the same is happening with BW. When I bought my sop about four years ago it was £350. By the time it had been manufactured, quality checked, packaged, sent from China to the UK, import duties paid, final set up done and a slice for the retailer, I can't see that there is much left over for the manufacturer's profits. Even with Chinese labour costs, there's just not much profit margin. However, the brand has been a big success, and now that a bridgehead has been established, I can only see the brand being steadily priced further upmarket. The same sax now costs £650. That's not just an inflationary price rise, it's a strategy to establish a brand by selling at very tight margins for the first few years then reaping the benefits thereafter.