I've never used Mandriva myself. It used to be a very popular distro, in fact at some time I think it was probably the most popular, at least on the desktop. However it has suffered over the past five or so years. I have always heard good things about it though.
I would take the claim of best hardware support with a pinch of salt. Most distros are equal in this. As for the difference in versions, the free one is 100% Free software, while the other versions have proprietary software and drivers built in. I doubt you can get Mandriva-developed proprietary stuff anywhere for free (legally) but I would bet that third-party drivers and such are available. With distros like Mandriva, if you pay money you're generally paying for little more than convenience.
Give the free version a try by all means, but unless you're running a data centre I see no reason to ever pay a penny for Linux.