Choose a distro that doesn't have middle-men between the packages you use and upstream open source. Like Fedora or Debian. For what I mean by middle-men, I'll give a counter-example: Kubuntu, that is based on Ubuntu, that is based on Debian, that is based on upstream projects. I think that these chains add unnecessary complication to all parties.
I recommend Fedora due to the superb packaging done by the Fedora community (and supported by Red Hat giant). And if you like a desktop environment like KDE, you can just install it, or start straight from their KDE Plasma Desktop spin.
Not a good example. Kubuntu uses the same package repository as Ubuntu just installing different desktop packages. Also Ubuntu is used much more than Debian so its packages get more in-the-field testing. Xubuntu is my standard default or Ubuntu with LXDE for mobile tablet-sized laptop.
I recommend Fedora due to the superb packaging done by the Fedora community (and supported by Red Hat giant). And if you like a desktop environment like KDE, you can just install it, or start straight from their KDE Plasma Desktop spin.