Best Choice for Small Subwoofer

[M3Shark]

Hi everyone,
I'm looking to pick up a subwoofer to add to my system. I live in a small apartment, so overall size of the sub is important to me. Currently I have no subwoofer, so I am in desperate need of adding some bass to my system. With that being said however, I'm not on the bottom floor of the apartment complex, so overall power is not that important to me, since I won't have it cranked up anyway. My budget is no more than $200 shipped to me.

I'm considering the following(plus any ideas you have):
Energy ESW-C8
Energy ESW-M6
Lava Subs 8in
BIC America V80

I'm leaning towards the ESW-M6, since its the smallest, and the most powerful(for future possibilities). But is it too small to create good quality sound?

Current system is nothing top of the line:
Onkyo TX-SR507 AVR
Polk Audio RM8 Center channel
Phillips generic HTIB front and surround speaker

Thank you for your help.