I generally prefer Debian-based rather than Red Hat based, in my experience Debian-based ones (especially the package managers) are easier to deal with.
Yeah...I'm not quite a fan of the yahoo search change, but it will get them more money, and you can always change it with a couple of clicks. I've never really been a fan of the deafault ubuntu theme myself, I've always changed it. I'm not sure I like the direction GNOME is going with the whole GNOME shell thing...I'll probably be sticking with the good old panel for a while.
Ubuntu is what I started on and is my main one, but I keep 4 partitions with other random operating systems I happen to want to try out, right now I have openSUSE, Arch, a 32-bit Ubuntu, and then an XP one I avoid like the plague. I generally never need to use it since my few windows needs are usually convered by wine or with my Windows 7 VM inside VirtualBox