FreeBSD. (Ok, not a linux distribution, but it's an alternative to using a linux distribution.)
Much of the difference is subjective. FreeBSD feels coherently designed, whereas Linux is a patchwork of programs written by different people with different styles and philosophies.
I don't know a lot about Gentoo (most of my experience is with Debian and Slackware) but from what I understand, its purpose is to be as flexible as possible. That's a legitimate goal, but it seems to conflict with ease of use.