The question is, for what site is this skin going to be used? Most of the skins you linked are nice in many ways, but it's impossible to give a proper assessment without knowing the context of the site on which they will be displayed
None of them jump out and say "this is where the guys hang out and talk about guy things." Most of them look like sci-fi, gaming or techy skins. They are very nice, they just feel way out of place for what you're talking about.
If I was forced to choose, I would say #3 works best, then maybe #5. Those are the most "general" looks for a "general" forum.
I personally like the 3rd one and the default one, because all that eye candy isn't necessary on a forum. Your main goal is to promote usability to make people sign up. I don't like the side bars because it squeezes the main forum in. Also, I don't think the purple one would be good for a guy based forum. Good luck.