What is the best subwoofer you have ever heard?

By far and away Servo-Drive Tech7's.

For powered in home use nothing comes close to the Velodyne 1812. I heard a pair supporting a pair of Avalon Sentinels. Sounds like sever overkill but the presentation was sedately stunning.

For HT you could save a great deal by using any formidable sub without EQ/room correction since the HT processor would be handling those duties.

I had a REL Studio III, JL Audio 113, and a Velodyne DD-18, in the house for a side by side comparison a few years ago. The JL and the Velodyne were clear standouts.

Mat, I've never heard the Paradigm but considering your needs I doubt it will fail to impress.

IMO, a good subwoofer can do both HT and two channel very well. To accomplish this with sensible connivence the sub needs some form of modern signal processing with presets that can be switched via a processor, pre/pro, receiver, or subwoofers, remote.

Even if its a dedicated HT or a two channel system the media usually needs its varying share of EQ such as phase or gain. The more control you have over your sub at the listening chair the more you'll realize just how important a sub can be.