Yesterday Ubuntu marked it's 10th birthday, quite a landmark since there many other distros that have come and gone during this time. Personally I've been using Ubuntu for the constantly since the 10.04 LTS Lucid Lynx release.
I've just stop using Ubuntu for a about 4 mouths, when I tried the cinnamon shell variant of Linux Mint 17 LTS Qiana. Though I liked Linux Mint, it doesn't quite feel as right as Ubuntu does for me. The Unity shell fits the bill for me on how I expect my desktop to look and work.
When the move was made from GNOME to Unity on the 11.04 Natty Narwhal release, I was somewhat doubtful about it. I really liked how GNOME work, even though it didn't feel as well as Unity does now. If there was a moment where I could have jump to another distro, it was then. After more of two years of using Unity, and seeing it getting better over time, I must admit that it was become my favorite shell out there.
I freely admit that Ubuntu is far from perfect, but it's the best distro for me since it gives me the best user experience. I gave GNOME 3 a spin as soon as possible when it was available on the Ubuntu 10.10 Maverick Meerkat, and it didn't like it that much. I could have grown to like it, but it really didn't do much for me.
Unless something cataclysmic happens on future releases, Ubuntu is my go to GNU/Linux distro.