Velodyne has always made a good sub... if I were going to choose between these two, I'd definitely choose the Velodyne. Dayton is your basic generic Parts Express sub... probably an okay sub for the money, but most likely not in the same league with Velodyne.
I'm assuming you have found this Velodyne at somewhere around $275-$350.
Consider spending just a tad more and getting the SVS PB10-ISD. I think there would be a world of noticeable difference.
If there is just no way to afford the little extra, go for the Velodyne.
You can see a review I did earlier this year of the VRP-1200 and a few other subs at the link in my signature. Can’t speak for the Dayton, but the 1200 wouldn’t be a bad deal at the lower end of the price range Sonnie quoted.
It’s not that great with music, because it’s a little bloated and therefore doesn’t render bass detail well at all. But it’ll do okay for home theater - in a small room at least. With some equalization the 1200 will hit 25 Hz in a small bedroom-sized room. In houses with large, open living rooms it probably won’t get better than 30 Hz.