i always recommend seasonic power supplies to people first and i also have the m12II 520w and 620w for 2 years now + an x750 for a few months. no noise from any of them AT ALL and still running strong
Why do I love Seasonic power supplies...? Because they're the best power supplies out there. The very best power supplies from Corsair, Antec, PC P&C, Silverstone and XFX tend to be rebranded Seasonic units. Why not just go directly to the source?! I'm using an X750 that is FULLY modular (even the 20+4 pin connector) and still is able to maintain it's 80 Plus Gold rating, which I find pretty impressive. I would of course love the chance to upgrade.
I've always liked Seasonic PSUs originally because they were among the coolest and quietest running PSUs besides being rock solid and awesomely efficient performers.
I have had an S12-600 for ages now. It still runs as good as day 1. Nice, quiet supply with low heat output. Seasonic is definitely my first consideration for power supplies now.