I prefer Mint mainly because of the decent looking initial theme, and the superior driver support. I've almost never had any issues getting Mint to install properly with everything working on the first try. Also, the install and configuration process is extremely streamlined and easy to follow. Not that Ubuntu is bad, per se, but Mint seems marginally better.
I'd definitely recommend Mint first for someone not yet well acquainted with linux. The ease of install, simple menu, and software installation tool make it a lot nicer on new users.
I run a virtual boxed Mint in seamless mode on Windows 7 continuously, to use as a shell for ssh and programming in certain languages (like arc or c), and I use a heavily modified Mint on my netbook as well.
