LOVE the LVX12. I just received it last week and I'm planning on posting some comments after spending more time with it, but so far I'm totally impressed and happy. My room isn't that big, 12x16x8, and it easily fills the room with bass and can make the couch and walls shake. The first movie scene I tried with it was War of the Worlds when the ship emerges from under the street. The output was so much that a cover panel that hides access to a shut off valve came off one of my walls. However, the thing that impresses me the most is how tight and accurate the bass is, and it really shines for music much more than I expected. The tighter bass actually helps the sub integrate into the music more and disappear, increasing the sound stage, especially in depth. I had read this from other people who had initial impressions with high quality subs and I was always unsure of what they meant and how the sub would impact the sound stage and imaging, but now I get it! I was coming from a Reaction Audio BPS212 sub, which has dual opposed 12" drivers and 300w in a sealed box. I was close to buying an LV12R but then the RA sub came out and I thought since I want a musical sub, getting something sealed would be good, and it was a promo for only $400. However, the performance difference isn't even close. I upgraded because I wanted something to dig deeper for movies, but I didn't expect the LVX12 to be so much better for music, but like I said, not even close. I had thought about trying to integrate the BPS212 into my HT with the LVX12, but now I'm just going to sell it. I don't want to degrade the sound at all and the LVX12 is plenty of sub for me.
I don't think you could go wrong with either of the 3. I upgraded to the LVX12 from the LV12R because it was on sale and I wanted the front ports since space is a bit tight in my room, but I bet the LV12R would have been plenty too. Of course, if you can fit and afford the 15" then go for it! You can't make a bad choice here.