Ubuntu's a great start if you've never used Linux before and you want a system that's really simple to use.
When you get bored of Ubuntu, maybe try Debian. My favorite's Slackware, but that's not as newb-friendly as some distros... Debian and Ubuntu are great for beginners because they also have good package managers and stability.
If you do want to use Ubuntu, I'd recommend either Ubuntu Mint or Xubuntu. I haven't used it seriously for a few years, but it shouldn't give you too many problems. Xubuntu has a more classic interface than Unity and a slimmer interface than GNOME/KDE.
Good job on thinking about switching! I hope you enjoy the GNU/Linux experience!