Gentoo because it is as stable as Debian, less bloated than Arch, has more packages than Ubuntu, is rolling release, can mix and match stable, testing and unstable on a whim.
Even its one downside, compile times, is now gone if you just choose to use binary packages.
I agree with Gentoo.
I had installed Arch for my wife, to get fast install times and more normal user friendly upgrades, but it kept breaking all the time.
It really opened my eyes to how incredibly stable Gentoo is while still allowing living on the bloodiest of edges at the same time.