Ubuntu is my favourite.
- Good forums with a lot of info from other members that report their experiences with hardware support and later move this info as formal wiki that has helped use the most from a few laptops that often required additional fine tunnings for some hardware components.
- Simple and clean interface, wasn't a big fan of gnome as default but eventually started liking it more as time passed.
- true 3D experience (same as other linux flavours) but this is a plus when moving away from windows OS
- huge repository, makes it quick and easy with .deb and synaptic to add programs and keep things tidy and updated very often.
- good active directory integration - no hassle when trying to use shared folders on remote windows locations or permissions
- free
(and free CD's sent to your home!)-------
Cons:
- don't know yet how to add new drivers for components that are not mentioned anywhere
- without internet there isn't much chance of learning how to solve your troubles
- doesn't fully run windows apps (but I've installed virtual box to solve this matter)
- need to learn how to use a command line window (console)
- sometimes, I fell a bit dumb because I don't know yet how to do things as well as I do them in windows.
- more work to install components such as flash, java and other because they don't come installed as default
------
Nevertheless, no windows is installed on my work machines and I'm very happy for using and learning my way around these difficulties because it brings freedom to my work methods.