I'm using the finished version of the Johto Elite forum style. What I don't like about it is that some members make their text color black, and it's annoying to read it. Other than that, there's nothing that really stops me from using this. It's one of the better forum styles out there, and I can tell that it took a while to finish it.
Recently, I've been using forum styles such as Route 167, Inverted, The Plaza, and Final Resistance. Route 167 is a special forum style in my case, because I tend to not use any fixed-width styles. Making everything cramped into a small box is not something I prefer. Its design and colors won over me, however. I like Inverted because its one of the few, dark forum style that I use. I think the banner for The Plaza is just cute. Using Final Resistance reminds me of the good times I did here when first using it.
My favorite forum style has to be Infernal Smash and Conway. Both themes are amazing on its own, but are barely recognized. The banner for Infernal Smash actually contains the stock of an actual Infernape, and not some chibi of it. Conway's layout and colors are dull, yet still appealing at the same time. Those two forum style are also the first two that I have ever used.