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I happen to like Fedora running KDE.
Gnome is a mess right now, and Xfce is missing some configuration tools. KDE on the other hand has matured nicely.
Red Hat has some good release engineers, and they rarely break stuff.
Ubuntu has release engineering problems, and stuff breaking isn't user friendly. It does have a big presence in the consumer space, so there is that. If we're just ranking them on technical merits, Ubuntu comes in second.
OpenSUSE's Yast is a complex mess, and I'm still not sure I completely understand what's going on there. OpenSuse does have the nicest desktops out of all the distro though, and if they could streamline Yast they could be at the top.
Best Live Distro
I like Trinity Rescue Kit, since most of the time I'm going to be rescuing data or cleaning a virus.
The Fedora Xfce Spin is second. Slax used to be my second, but the project kind of stalled.
Best for Older Computers
I'm still tinkering with this one. I have a two old Pentium M based laptops that I still would like to use, but I haven't found a good one just yet. Debian is okay, but I'm thinking I'll check out something from the Slackware line when I get some time.
Best Office Desktop/Best Support/Most Stable Across Releases
Scientific Linux for a free stable Linux desktop with long term updates, Fedora for free Linux desktop, or Red Hat for a stable Linux desktop with long term support and updates.
I know I sound like fanboi, but Red Hat really does produce nice stuff that works. If they didn't, I would have moved on to something else
As a bonus, third parties support RH distros.