The only way to know if something sounds "right" for you is to go out and listen to a few!
I've got a Blueflame turbo-back with sports cat. It still has the middle resonator but the suitcase box at the back has been removed. I think it sounds excellent, and I was very happy with the price I paid (tho about 2 weeks after I bought it they did a group buy for about £150 cheaper
). In terms of how it sounds, it is perfectly quiet when cruising (possibly quieter than stock), but has a nice throaty roar under load. Alex of AKS has heard it and said he likes it, and I'm sure he's heard a few in his time.
I've heard great things about the BCS Powervalve, and I have no reason to doubt it is an excellent product. However, it is a fair bit more expensive than what I paid for my Blueflame and I'm not 100% sure that it is worth the extra, despite probably being a better product.