Site specific signup, any day, with long lived cookie remember me. Way too many companies view my FB credentials as a way to market themselves to my friends rather than as a convenience to me.
+1
Personally I find the whole idea of relying on a third party site for sign-in a bit odd. Let it be Twitter, Google, Facebook or anything else... there will always be people, who don't have an account for that specific site, don't want one, or don't want to let the site's owner know what their name on that third party site is. Another problem: aren't Google and Facebook blocked in some countries like china?
Again, the whole idea doesn't work out in my opinion.
