What's the best Sub ??

The best sub? Love a meatball sub!

Sd has given you a good list. The REL Q subs may be preferable for a dedicated HT system. The HSU VTF subs are also good for so little $$$.

I suggest you look in the A-gon archives -- there have been many threads on this subject over the past 4-6 months. You might find it helpful to look for an article I submitted which summarized the results of subwoofer tests done by Widescreen Review magazine. My post gave the ratings for the top dozen or so of the subs rated by WR mag.

The consensus about the "best subs" by many of the regular readers on this forum would include:
1. REL Storm or Stadium
2. Vandersteen 2Wq or V2W
3. Revel B15
4. Velodyne 15" or 18" models
5. Bag-End 18"

If you are limited by budget or available space, then you might also want to consider the Sunfire True Sub, or the Hsu 1220.

Best regards.

You don't mention price. If your bedget for a sub is at or below $4500, then you might consider Aerial Acoustic's SW12 12 inch sub. If your budget is around $2k or less, then you might want to look at the Bag End Infra-sub or the Triad Platinum 18 inch subs.

The Bag End and Triad retail at $1600 and $2000 but you may find them used at just over half price. Both are quite musical.