Ubuntu's good. I made the switch to Ubuntu 9.10 about a year ago. It took me a few weeks to make it decent enough to use as my main OS - For example, I like sharp aliased "xp" fonts - and finding proper replacements for my apps took a bit.

Personally, I like the KDE desktop - it's more 'windows' like than even windows is, and combines with desktop compositing via Compiz Fusion... It's far more usable than xp or 7 is.
(I can't live without my 4 virtual desktops mapped to F9-F12).

I have become a fan of the command-line, and often have a terminal open to do something or other. Shell scripts are also a major advantage - I have pair of them doing on-the-fly OCing /UCing of my video card, and I even have it setup to auto-oc when I launch TF2 via Wine.

These days, I decided to go with Debian Squeeze. It works about the same, but was a lot harder to setup - I may end up going back to ubuntu at some point.

I suggest Ubuntu/kubuntu to anyone - it's easier to switch to than others, and yet allows all the freedom of the linux world.