I'm super close to finalizing an mATX build. I've purchased much of the below pcpartpicker list, just haven't decided which case, PSU, and video card. My biggest question at this point is the power supply. I know I want a modular supply since the cases I'm considering aren't exactly known for their cable management (InWin Dragon Slayer, Fractal Design Arc Mini, Silverstone TJ-08). The below build is estimated at ~380W (I put in the 7950 since I'm pretty sure it draws more than the GTX660ti and GTX670 I'm considering... worst case scenario):
Any of the ones you listed should do OK, though. Most that are $1 per 10w are built pretty well. I just trust the ones I listed more. Out of the ones you listed, I would probably go with the SeaSonic one.
It is the best out of the ones listed, and probably better than anything else in its price range.
This is because it is the most efficienct: 80 Plus Gold efficiency vs 80 Plus Bronze at best for the others.
It has independent voltage regulation, the only other unit mentioned which isn't group regulated is the XFX 650W.
It is modular, which the XFX and Corsair units aren't.
It uses nothing but Japanese capacitors, only the Seasonic M12II Bronze 520, Antec HCG-620M and the XFX units also only use Jap caps.
It has a 5 year warranty. The only other units which also have a 5 year warranty are the Seasonic M12II Bronze 520, XFX 550W & 650W. Others are 3 years.
It has the slowest spinning fan and therefore the highest chance of being quiet. It's fan is capable of spinning up to 1200/1500RPM, but most likely it will be remain at 700RPM even at full load.
The others might start at 600RPM, but by 50% load they will be over 1000RPM and by full load some of them will reach 1800RPM.
I hope to illustrate with the list above that some competiting units can match the Capstone-550M in certain aspects, but not all aspects, therefore it comes out ahead of everything else.
Thanks Silvune! Between your post and Raiddin's post, I've pretty much narrowed it down to the Rosewill vs the Seasonic, leaning towards the Rosewill. Gonna keep my eyes out the next few days for any price drops though!