If you want maximum commodity and as many things to "just work" as possible out of the box, go for good old plain Ubuntu.

If you care a little more about your privacy and is willing to sacrifice some commodity, go for Fedora. It's community run and fairly robust. You may have issues with media codecs, nvidia drivers and few other wrinkles though. The "workstation" flavor is the most mature, but you may want to give the KDE version a try.

If you want an adventure, try everything else people are recommending here :)