Which subwoofer should I buy? Help Please

Looking for a good powered sub with small footprint.

Have the following in mind:
Earthquake MKIV10
Sunfire True Sub MK II
Sunfire True Sub Jr.
Carver Knight Shadow
Yamaha YSTSW-215

Earthquake is the biggest I will go (14" cube)

Sunfire True Sub MK II, I heard it's slow and not good for music?

Sunfire True Sub Jr., I favorite this one the most. Smallest footprint, 9 inches cube, but quite expensive...
How much do they usually go for (for used ones)?

Carver Shadow Knight, made before Bob left Carver. Also a subwoofer with a super long throw driver. Extremely similar with Sunfire subs. Sells for only $300 used and if it perform like the Sunfires, it will save me some money.

Yamaha YSTSW-215, cheapest, heard they are okay. I might need 2 of them if it's not enough. Will still have money left if I buy 2... Sounds good... but sound-quality-wise?

Really don't know what to buy. $550 is the max I can afford... Please help...
What kind of speakers and amplifier do you have? Post your system.
Mostly for HT use, I have Infinity throughout my HT set up.
I've heard good things about the Knight as well. That may be the way to go, but at $550 price range, Paradigm deserves a look. They are pretty solid subs for music and theater.
Where is velodyne in your list? My velodyne is much better than my old sunfire. Beats the sunfires hands down! If you want tiny with a lower price and a little less power, pinnacle baby boomer is nice.
REL Q201E is 12 inches square. It cost over $1500 new, but I've seen used ones for $700 to $800. You'll think you have a large footprint $2000+ subwoofer with this one. It might be worth a stretch in your budget.
Take a look at James Loudspeaker EMB-1000, about $1500.
Check out Martin Logen