What is the forums opinion of SVS subs?

I use a SVS PB2000 pro sub with my JBLL100 Classic speakers and the single sub really made my system go from pretty good to incredible.  Like others have said, their software to integrate the sub is excellent and easy to use.  You can make adjustments on the fly too. I was going to add another of the same sub but the system sounds so good with one, that I don’t want to spoil the magic. 

Compare the warranties before you decide.  BTW, I've owned 2 SVS subs and both were problem-free.

the REL is probably the most musical sub on the market, integrates extremely well with your speakers.

I have the svs sb16 ultra it took a little more work to tune them with my tekton's than my klipsch but once I got it there you can' tell where the sub ends and the mains begin. I also got the svs isolation feet that work really well I have also put them on my tekton's. The 1 sub gives me more than enough bass.

I haven’t listened to any REL subs. A few months ago,I was looking to upgrade my aging HSU subs. I had my initial search down to Rythmik, REL, and SVS.  A deal for two SVS SB2000 pro’s popped up that I simply could not walk away from.  My take is these were a bigger upgrade than I had expected. They were very easy to set up, and definitely do everything I need them to do.  Unfortunately,I can’t comment on the others,but they do get rave reviews just about everywhere.