I think the comments board on here is generally pretty good. Kinja is not perfect, but it's better than many others. There are some forums out there that are truly, truly awful.
Among the Gawker sites, I would say io9 isn't bad, Gawker is not great, and Kotaku is probably the worst (I haven't got enough experience on Deadspin or Gizmodo)
On the larger net, IMDB is pretty awful, and Youtube is of course notoriously bad.
But for me, the worst is probably HuffPo. The thing about trolls on IMDB or Youtube is that they're usually either driveby trolls or else they get into such specific, weird arguments that you can avoid them. But HuffPo...