From a physics and engineering standpoint the SVS subs are some of the best subs you can get regardless of price. For the money they sell them for they are a steal. I owned one a couple of them for a while before I got into building my own subs and working on infinite baffle designs. Never, ever buy a sub with a small box, the lowend output drops off dramatically. To get low bass you have to have a big box and a big woofer with a lot of excursion, and preferably a lot of power too. Anything that uses a small box is going to have pretty serious compromises in low end performance. I define small box as anything with less than 18 inches per side of the cube, depending a little bit on the T/S parameters of the woofer.
Oh yes, also set aside some $$ for a good parametric EQ, as there will be large peaks and valleys in sound for the bass, which are the result of the dimensions of the room you have the sub in. You can't do much about the suckouts (valleys), but you can very easily control the peaks. These peaks are usually the reason bass can sound "bloated" or overpowering in a room. By measuring and eliminating them, you get much cleaner and tighter sounding base, while still getting gut-wrenching low end power. You'll need a sound meter with an analog, not digital, readout, and a cd with test tones closely spaced from 20hz to 100hz.
One other tip - the location of the sub in the room is critical to good sound and performance. Usually the corners are the best place for a sub, but not always, it's very room-dependent. I recommend sitting in your primary seating position and put on a bass heavy song with the sub in one of the room corners. Listen closely to it, then move the sub to a different corner and listen again. Then move it to the middle of a wall halfway between the corners and listen again. Iterate this out until you've tried all available locations for the sub. Give the sub a permanent home in the location that sounded the best from your listening position. Only after it's in it's permanent home should you monkey around with the EQ and the sound meter.