I use Gentoo. Why? Because when things go wrong, I find Gentoo is easier to fix than any other distro I have tried. And lets face it, things go wrong!
If I just wanted "an install and use distro", I would probably use Debian or Ubuntu. For my personal systems though, I like the option of removing packages I no longer need without serious risk of breaking my package manager. I want the option of being able to update and still change the packages installed without major hassle. In general, I want a package manager that functions well. RPM failed when I tried it, Debian had other problems, and Ubuntu wasn't really on the scene back when I started.