I have listened to REL and I have listened to SVS. All the REL subs seem very refined and when set up correctly, blend in seamlessly. The only drawback I have found is price. They are a bit expensive, but I really like the whole line. 🙂
SVS is another animal. For home theater they are fantastic! The pricing is fair for what you get. But for critical two channel listening I would not look at SVS. Oh and both have great customer service.
Sorry I can’t help you with any other brands.
JD