Most important stat is voltage regulation. It takes better construction and design to hold voltages within a 1% range under all loads. And dock points for units that artifically inflate the zero load voltages up to the max allowed under ATX specs, such as starting at 12.5V for the +12V rail.
Second is ripple/noise suppression. Lower ripple/noise suppression figures are always preferrable to looser figures, but if it's within specs, the unit with tighter voltage regulation will get my vote.
Not much difference in performance between units with 10mV ripple differences (such as 35mv vs. 45mv, both well less than half ATX spec and won't show any real world performance differences), but a lot of difference when one unit has 3% regulation.
Third is efficiency. There are a slew of power supplies out there garnering Gold certification for efficiency but have horrible electrical performance.
Fourth is fan noise. Honestly, if fan noise is such a concern, buy a fanless unit like the Silverstone Zeus line or a Seasonic X-series (fan doesn't operate until half power draw placed on it.) Outside of PC Power and Cooling's leaf blower Turbo Cools and Silencers, fan noise isn't much of an issue for performance computers. Granted, for a completely silent computer, it may be, but the vast majority it's a metric that's almost irrelevant with the large, slow turning fans used on power supplies these days.