My preferred distro. is Linux Mint. When Linux Mint was first launched in 2006 it was no more than a few extra repositories bolted on to Ubuntu. I first used Linux Mint when it was release 3.0 and based upon Ubuntu 7.04 (see below)
http://news.softpedia.com/news/Test-Driving-Linux-Mint-Cassandra-56041.shtml
Back then direct comparisons could be made however these days although Linux Mint still uses Ubuntu repositories it is the only thing the two have in common. Otherwise they are utterly different so you might as well be asking OpenSUSE vs Fedora ! Thats literally how different Ubuntu and Linux Mint have become.
The best of the bunch is Linux Mint 9 without question plus it benefits from the Long Term Support of Ubuntu 10.04
An interesting release to take a look at is Linux Mint Debian Edition. It requires a little more thought when working with than its Ubuntu based sibling but remember Ubuntu was originally derived from Debian in any case (mention this to any Debian purists and wait for the scorn to head your general direction)
http://www.linuxmint.com/edition.php?id=66
Having said all this I am not saying Ubuntu is inherently bad however its had its glitches down the years (most notably 8.10) which was truly awful on release and Linux Mint 6 suffered the knock on effect and only became good just prior to the release of Ubuntu 9.04 which was outstanding and also the last release to use ext3 and grub-legacy. After which everything became ext4 and GRUB2
Linux Mint releases and the Ubuntu releases all of which I have worked with
Mint 3.0 (Ubuntu 7.04)*
Mint 3.1 (Ubuntu 7.04)*
Mint 4.0 (Ubuntu 7.10)*
Mint 5 (Ubuntu 8.04 LTS)
Mint 6 (Ubuntu 8.10)*
Mint 7 (Ubuntu 9.04)*
Mint 8 (Ubuntu 9.10)
Mint 9 (Ubuntu 10.04 LTS)
Mint 10 (Ubuntu 10.10)
*denotes obsolete
Currently running
Linux Mint 10* (kernel 2.6.37/Nvidia 260 and Firefox 4.0 Beta 7)
http://www.linuxmint.com/edition.php?id=67
Linux Mint 9* (kernel 2.6.37/Compiz 0.8.6/Compiz 0.9.2 compiled in C++/Nvidia 260 and Firefox 4.0 Beta 7)
http://www.linuxmint.com/edition.php?id=52
Linux Mint 8* (Compiz 0.9.0 compiled in C++ and Nvidia 260 on a Custom LiveDVD)
http://www.linuxmint.com/edition.php?id=44
Linux Mint Debian* (Compiz 0.8.4 and Compiz 0.9.0 compiled in C++ on a Custom LiveDVD)
http://www.linuxmint.com/edition.php?id=66
Windows XP Professional SP3
LUg.