Since I installed Ubuntu on my main computer in February 2008, I have pretty much been an Ubuntu devotee. If your goals are to get most any computer working out of the box without a lot of tracking down of proprietary drivers and the like, Ubuntu is probably your best choice. I have spent a great deal of time over the last few years advocating for the use of Free and Open Source alternatives to proprietary software, particularly to library staff, as libraries are my professional milieu. When a Windows user I know is wanting a change from all the strife that comes with running Windows (and needing an upgrade), I always, without hesitation, recommend Ubuntu as their solution. I have also been very active on the Ubuntu Forums and the #ubuntu IRC channel on FreeNode (username yeats on both), assisting new users with problems I know the answers to.
However, as a Linux user myself, I've been feeling the need for a change. I still primarily use Ubuntu on my home and work desktops, but on my work laptop and Dell mini, I have been experimenting with Fedora (first Fedora 14, and now on Fedora 15). In the Linux world, Ubuntu is undoubtedly the most popular desktop distribution, but it's always followed closely by Fedora (often vying with Linux Mint for second place). Both Ubuntu and Fedora use GNOME primarily, and they are both quite polished (nice fonts, consistent display, well-designed backgrounds, etc.). Up until this spring, the desktop environments were very similar overall. The recent moves to the "next generation" desktop environments (Ubuntu to Unity, Fedora to GNOME3), has made the choice more about which environment you want to work in. Without getting into a full comparison of the two (which has been done to death all over the web - enjoy Bruce Byfield's evaluation here) or into the "Canonical vs. GNOME" drama, I will say that 1) I was not happy about the "taking my toys and going home" attitudes I saw from Canonical, which is a slight on the entire Ubuntu project, unfortunately and 2) I stopped using Unity, preferring "Ubuntu Classic" (calling up some nostalgia for me) after a couple of weeks for usability. Using GNOME3 has been a pleasure so far.
I'm sure I'll report more as I begin to transition from Ubuntu to Fedora on my primary desktops.