Search for threads talking about flame wars. That's the worst question you could ask here. Answer: TRY IT OUT YOURSELF AND SEE.
Nobody can tell it to you, but everybody will try. Believe who you want, but there's a 50% chance s/he is wrong.
Trying out a live-cd is the easiest method. Ubuntu Desktop cd/dvd is a combined live+install disc. Not sure about Mandriva, but I hope it has live-disc edition as well, so people can try it without installing. Mandriva is an rpm based distribution, like Fedora, Ubuntu is a deb based distribution, like Debian. They're both good, easy, nice, beautiful, powerful, newbie-friendly, server-capable and everything you want. It's just that their configuration ways differ a bit (different kinds of filenames and upgrade tools and such), but essentially there is no big difference. You get the same desktops, wallpapers, themes, programs and everything for both of them.
Last edited by b0uncer; 07-27-2007 at 03:18 AM.