I would actually recommend Mint (if you going the Ubuntu way) for a first time user.
Actually, I would say try anything except Ubuntu first. The reason being is that the majority of new users migrate to Ubuntu within a year and stick with it for a long time (till they discover Arch).
You need to experiment with a couple of distros first as they all teach you how to be a better Linux user.
(Anyway, Ubuntu One is still a ****. Been one of there first users and they still cannot get close to DropBox. Its just a damn CouchDB instance - how hard is it to get it working !!!)
Love Ubuntu
1 Ubuntu 2196
2 Fedora 1455
3 Mint 1381
4 openSUSE 1231
5 PCLinuxOS 1004
6 Debian 1002
7 Mandriva 863
8 Sabayon 745
9 Lubuntu 736
10 Arch 729
Damn...
The last distro's of linux I used were Slackware and Red Hat 7.2 :/
I need to get with the program...