Gentoo works best for me because I'm a control freak. It lets me tune my system in any way I want, and I don't mind leaving my computer on while I'm asleep so that it can compile its way through libreoffice, webkit, and a couple of browsers. Plus, based on complaints I hear from people using other distros, Portage beats other package managers in every way except speed.
This doesn't mean that it's best for everyone, mind you, just that it's best for me.