What is the best subwoofer you have ever heard?

I've had a Paradigm servo 15, good sub. M&K MX-350 MK2 in really cherry wood. Good sub but just didn't have the low level extension. I now have a SVS PB13 Ultra and at 2 notches on the volume and -15 on my pre output level it is dynamicly robust .i do want to compare it to two SVS SB13 Ultras as I would like a smoother response and two will give tighter, faster bass.

If I were you, audition two SVS SB13 ultra subs - 45 day trial. I have a PB13 Ultra(best sub I've owned and heard) and i'm going to try a SB13 Ultra, decide which I like better , and get another of choice. Depending on your room size, 2 SB13 Ultras cost you the price of one JL audio F113, 4 will cost you the price of a Paradigm Sub 2 in price. If cost is no object, I'd get 2 Paradigm Sub 2's and calibrate them and be done.......so done.......