What is the forums opinion of SVS subs?

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. 

I had one SVS SB-12NSD and was very happy with it. But I kept reading here about people using subwoofer swarms (4 subs) and raving about it. I stumbled across a guy selling two of that same model for $400 for the pair and jumped on it to see what all the fuss was about. While that doesn't give me a full swarm the difference in bass quality is remarkable, truly fantastic. In fact is has improved the entire sonic presentation. So the hunt is definitely on for a 4th.