I have done CRAZY research about this for my own build and I picked Seasonic.
Antec = Quiet, VERY nice voltage regulation. VERY tight.. like +/- 1%
OCZ = Moderate for noise, fan may make whining noise. +/- 2-3% regulation. Great that cables are shielded/twisted?
Fortron FSP = FRIGGN LOUD. This thing ramps up too fast for the fan. Regulation is decent, but I like the shielding. Fan goes full blast by the tiem you hit 250 W. Even 200W is hella loud
Seasonic = MY PICK. I have a 600W Seasonic. It's beautiful. Rock solid rails, very VERY quiet. Regulation is not as tight as Antec, but tighter than OCZ or Fortron from what I read. My measurements show 11.98v idle and 5.01 idle. Didn't test load, but +/- 2% is great. My only complaint is that the 12V rail is not as strong as say the Antec. You only get 18A per rail on the 600W and 16/17W for the 2 rails on the 500W. Antec gives you 18A already on their 480W model.
I warn you that Seasonics MAY HAVE problems w/ DFI LanParties. I have one myself, and I never had a problem. My friend however could not boot at all w/ his SEasonic.
MY decision was really between Antec and Seasonic because both are awesome PSUs, but Seasonic was quieter and it had twisted cables while Antec didn't.
I listened to the sounds on Silent PC Review and Seasonic wins HANDS DOWN.