If you were primarily listening to music, the HSU, BIC (HSU design) and Emotiva subs would all be great choices. But you said that this is all about movies and games, yes?
With movies and games, playing as low as possible and being able to play with great dynamics tend to be the more important characteristics. By no means are the STF-2, PL-200 or Emotiva subs "bad" subs. But none of them really focus on playing low. Instead, they've gone for better accuracy and nice impact in the 50Hz and above area. That's really important for music - more important than playing super low or loud. So those subs get a lot of praise because they are "musical" subs, but playing really low and giving you that awesome "hit you in the chest", "rumble your couch" experience isn't really what they're about.
The Elemental Designs sub is going to be a little better in terms of giving you better low bass impact. Out of the subs you were considering, and because you want this sub for movies and games, but not music, I'd personally lean towards the eD sub for that reason.
With your budget, it can be a bit tough to really get absolutely everything that you probably want. I would be remiss though if I didn't at least mention the $50 Auralex GRAMMA. Now, I don't know your neighbor situation. If you have zero worries about bothering your neighbors, then you might actually be better off
without the GRAMMA isolation riser underneath your sub! Normally, I'm all about reducing structure-borne transmission of sound. Whenever your sub plays, it shakes. And that shaking gets transmitted into the floor where it travels through the physical structure of your whole house! Sturcture-borne transmission is a big part of the reason why you can easily hear bass thump-thump-thumping away in other rooms (or in a neighbor's apartment). So normally, I'm all about using decoupling so that you will bother your neighbors or other people in the house a lot less and because it "tightens" up the sound that you hear in your theater due to reducing those wall/floor/ceiling vibrations and the distortion that comes from them.
In your case though, I'm betting that you're looking for impact and the sense that you sub is really shaking the room and rumbling with explosions and gunfire and whatnot. Having the structure-borne sound will actually heighten that sensation, even though it technically "muddies" the sound and makes it less accurate. With music being of no concern, you'd probably enjoy the physical shaking and "noisier" sensation of a subwoofer that is NOT decoupled via an Auralex GRAMMA.
If you have neighbors though, then a GRAMMA is a must! There's no sense in spending good money on a sub if all you ever get are complaints! You already said that you don't tend to listen very loud. But bass travels. Even at low volumes that your neighbors cannot hear, the bass will travel and still bother them.
So! No neighbor issues? I'd say not to worry about decoupling. Enjoy the sensation of rumbles and shaking with your subwoofer directly on your wood floor.
But. If you have potential neighbor issues, DEFINITELY get a GRAMMA. There is no question that your subwoofer is going to have structure-borne transmission in your case. You're going to be able to hear that bass thumping away in every room of your house. And if you've got neighbors close or attached, they're going to hear it thumping away too! A GRAMMA will greatly reduce that "bleeding" of bass and also give you "tighter" bass in your theater. You might miss the shaking sensation and the bass might actually sound a bit quieter with the GRAMMA in place. But it means more accurate bass. And, more importantly, it means far fewer complaints from the neighbors or other people in the house!
Hopefully, that description will let you decide for yourself whether spending $50 out of your budget will be worth it to you
