The Earthwatts is 80+ bronze certified which means it's very efficient at delivering power.
This will translate into savings on your utility bill.
Both units are good since the NEO has an 80+ certification as well.
I would go with the neo. First, its $20 cheaper and at only 2% more efficient then the neo it will take the earthwatts a long time to make that up. Second, the EA500D has 37A on the 12V rail while the Neo has 40. I doubt those 3 extra amps will ever help you, but they are there if you ever need them. Based on those two things only I'd get the Neo.
I would go for the Neo ECO 520C.
This PSU has been made by Seasonic.
It provides a single +12V output that is rated for up to 44A (480W) (a little more power than the EarthWatts green) . But it's not over current protected.
It has, like the Earthwatts green, one 6-pin and one (6+2)-Pin PCIe conectors.
It presents a bit less efficiency (80 Plus Certification) than the Earthwatts green. (It's the only other positive point for the Earthwatts green over the Neo Eco)
Same warranty: 3 years.
I presents a better quality capacitor in the primary: one Japanese cap from Chemi-Con (330µf 400V) rated at 85°C . On the secondary all the caps are Taiwanese from Su'scon.
It presents a better noise and ripple supression.
It runs a bit quieter than the earthwatts green due to its medium speed 120mm from ADDA.
Anyway, at the same price, I would go for the Earthwatts 500W (EA-500D "gray" model). It has a worse efficiency (80 plus certification) but a better built quality:
Above post - good comments.
To put 2% in perpective
EX Avg power consumption over 24 Hrs - 200 Watts (prabably high as assumes 24 Hour operation (Idle approx 100 - 150 Watts Load 300 -> 400 Watts and No hybernation while Sleeping.
Cost per KW/Hr 10 Cents (High side My cost is approx 7 cents)
(200 W * 2 %/1000) * 0.1 * 24 * 365 = $3.50 per year (Real life probably about $1.00 per year)
Thanks for the math retired, thats what I was hinting at. The fact that the Neo is $20 cheaper means you'd need the about 6 years of use using the $3.50 a year figure to break even. 6years from now your going to want to be using something else I'm sure. Add in the more power on the 12V rail and the Neo is a good choice.