Stamsorc, really? I am surprised to see so many votes for it. Is this like, consoles vs PC difference or? Open-world you have to pick your fights very carefully, or no dark deal will help. (Also I think better ssorc builds don't darkdeal for most of their regen). If you have no teammates and have to fight outnumbered, the under-voted stam dk is actually better than ssorc.
All this is not to say that you cannot be a strong stam-sorc. Honestly, the best answer for me is `whichever you feel like playing'. I voted magsorc to see the results, although I do think it is quite strong in open world.
Still depends on how you want to do it? Bombing a group? magblade. Facetanking and running around a rock? Probably DK.
I agree with nCats, rarely I have seen sSorcs that can 1vX on the level of Templars or DK. Honestly I rarely run into solo pvp'ers at all nowadays. However most of these votes happend several months ago. Don't exactly know when that hurricane nerf hit but the changes to regen, constitution and dark deal all touched stamina sorcs a bit.