I would get the Seasonics. They have been certified by 80-plus.org as being 80% efficient through their operating range, which has very real benefits, like a cooler-running PSU (less waste heat generated).
Fortron is also jumping on the 80% bandwagon with their new Green series (supposed to be 80%+ efficient too), plus Enermax has one that also claims to be 80%+... But for now, stick with the proven Seasonic, which also gives you the side benefit of being THE quietest fan-cooled PSU your money can buy.