I've built a few machines with the lower wattage 300-400 watt ones and they are still kicking and have never had any problems. I've also owned several Corsair HX models that were built by Seasonic (HX520, HX850) and the quality was top notch.
I need a higher wattage PSU to upgrade my current system right now, and would love to win one of these.
I love Seasonic PSU's. About 60% of the builds I have done for people are either Seasonic branded or Seasonic internals. Not once I have I had one go bad to date. Personally love the Gold series modular PSU's for excellent performance and reasonable price.
My favorite product is hard to choose, I like alol of the supplies with the hybrid fan control option, quiet is good! But the platinum 750 would be thebest in my book...
Every one of my Seasonic (or Seasonic built) power supplies are still working strong, but if I had to pick one it would be my X-1050. Runs cool, quiet, built like a tank, and the detailed wiring diagrams were invaluable for building my custom wiring harnesses.
I bought a Seasonic S12 430w for my Gf's system years ago and it's quietly and reliably powered all of her computers since. I have no hesitations recommending any of their PSUs.
My fav seasonic is currently the x750 in my desktop since the fan usually doesn't even need to run, but my server is running some cheap one that could definitely be upgraded!