I have administrated both the EE forums (for a very short time) and IP.Board forums (for a fairly long time), and I do agree that IP.Board is overly complex and bloated for most purposes. Unless your forum is the focal point of your site and therefore may require things like powerful social networking features, IP.Board is a waste. Forums for most websites are used for very basic posting, things any forum package can do. I seldom see any advanced features be used, to be honest.
My one general complaint with EE forums are its very basic permissions and grouping options. Unless I am missing something (and I may be, only used the software for a week or so), you are unable to assign members to multiple groups. This is something I sorely miss from IP.Board, as are IP.Board’s better title/rank features.
Basically, my main problem with EE forums is the generally weak group and user management features (I suspect this is due to the integration with the EE core software). Everything else is top notch and works fine, and the integration is so nice - lots of things you can do because of it.
Anyway, I’d go for the EE forums. They are inexpensive, work well, and integrate superbly (obviously). They have a few feature weaknesses, but they are mostly insignificant.
Oh, as for skinning the forums to match your main site, it is definitely not simple, but then no forum software is simple to do a complete skin for in my experience. The number of things that must be accounted for is huge, unless you trim things down immensely. Just changing the colours of the default skin to match is doable in short order, but a complete revamp that alters table layout (or better yet removes tables and uses pure CSS for layout), adds graphics, etc., is no easy feat.