Which sub should I get?

I now have a 2 channel set up on my end wall and a 10 year old RPTV on my side wall. As soon as my TV gives up I want to get a plasma to put between my speakers. I just found a center channel on Agon to match my speakers and now I need to locate a sub either a JL AUDIO F12 or a Velodyne DD12. Has any one had either or better yet both and which would you recomend.