Between 2.0 Aeris Reborn and 3.1 Oldskool for me.
Oldskool for the banner, and Reborn for the good color scheme.
I think I'm one of the only super hardcore 2.0 fans. It's my dead favorite because of the indented design. I like forums that are set to 60% of the screen, as you can see by... just about every forum I designed. I don't like if a screen stretches beyond 80%.
I even like the brown, I won't lie. I think if it was classic blue, more people would like it more, but I like the colors of the banner and they wouldn't match. I feel like brown is more warm.
I have to say though, I don't think this is a feature of any of our skins, but I really love when post information is displayed on the right and not the left. Like, the poster and the avatar and such. I'm not sure why, but I'm a really big fan:
<a href="http://s176.photobucket.com/albums/w200/ryechuuu/?action=view¤t=rightaligned.jpg" target="_blank"></a>
(Before the event forum was moved onto EoFF)
Maybe the powers that design may consider trying that in a future skin?
Originally Classic, but It got auto-changed to EoFF 2.0 back when it was implemented and I never bothered changing it permanently
there was a picture here
I use 3.1 without the banner and everything below the quick reply box apart from the theme switcher box.