Ubuntu is good at the core but the default version isn't that great. I'd suggest going with a variant such as Lubuntu, Kubuntu, or Xubuntu. As I already said, Lubuntu is my preference. Default Ubuntu has lots of unnecessary software, privacy/security-compromising software (such as Zeitgeist, which is hard to remove because of the dependencies of the file manager, text editor, etc), and an extremely ugly default DE (which is easy to change, yes, but just another disadvantage of the default version of Ubuntu). And the variants have the same repositories so the available software is the same.
Other good distros for people just switching from Windows are Linux Mint (based on Ubuntu and Debian) and Debian.