The best subs that I've actually heard in a demo are the JL Fathom and the Revel B15. Tight, articulate, fast, and authoritative bass. I liked it so much I got the Revel. The Fathom goes deeper than the Revel and if I had the cash would probably be the only other sub I'd go for. The RELs are the other brand that I would include in that as part of my top three.
I've previously owned Martin Logan, REL, and also auditioned (but not owned) Sunfire.
I've previously owned Martin Logan, REL, and also auditioned (but not owned) Sunfire.