Well, the enermax and seasonic both have 2 +12V rails while the OCZ has 4 +12V rails. For the money, i think the OCZ would be the best bang for your buck. And also, if for some odd reason 600W isnt enough, OCZ makes a 700W gamexstream version thats the same price as the enermax and seasonic if not cheaper, but go for the 600W one.
for the amps, heres a little chart/layout/thingy
OCZ: 4 +12V rails, 18A each
Seasonic: 2 +12V rails, 18A each
Enermax: 2 +12V rails, 18A each
So why pay more, for less total power? the OCZ has more watts, and +12V amps then both the seasonic and enermax and is cheaper.
I have the OCZ and its awsome. I kno i dont use all the wattage, but i like power