Hi, speakman. Outside of budget, what are your other needs/desires for the sub? The SB12-Plus is a nice sub, but its cost is driven a lot by its small size. If small is what you want, then it's a good pick. However, if size isn't a big concern, then a larger sub from SVS that costs the same or less would be able to outperform it.
I've had a lot of success when I've e-mailed SVS and asked them questions about their products. I'd suggest that you let them know what size room you have and what your desires are, and then ask them which of their products that they'd recommend.