@ salparadise
I would not recommend Ubuntu because they are diverging from mainstream Linux and you'll end up with some non-transferable skills
Seriously ? … such as ? … Ubuntut/Debian ARE the mainstream … the desktop interface is only superficial, and the skill set is MUCH deeper than that … att the end of the day even Unity is still mouse/directory/click driven, it’s only a layout change. ???
In all honesty I’d still suggest an Ubuntu based distro … if you don’t like the Unity desktop … either go with Mint, or change to “Gnome Classic” in Ubuntu … purely for the available help/support/documentation (not to mention PPA’s, Launchpad, etc. which can all ease the transition from Windows) but then thats just my opinion 
Though I DO agree, there’s no harm test driving other disto’s and finding the one that suits you best … and the great thing is, LiveCD/LiveUSB’s make that a doddle.
Here’s my take on distro choice for a beginner -
I’d agree, for the time being stick to the main distro’s …
RPM’s suck … so that’s Fedora out of the running straight away 
Mandriva … are they still considered a “main” distro, I’d be hard pushed to slag it off, but nor have I anything to offer as a reason to use it. (and as you say it’s French
) … Mageia on the other hand, maybe, but is yet unproven how easy beginners will find it, there’s certainly less online resources than Ubuntu based distros.
openSUSE … YaST is the worst piece of software I’ve ever come across, and HUGELY confusing for a beginner … I should know, it was what I first tried.
Debian … now that’s more like it, solid distro, easy to use/understand tools, great support … BUT their insistence of “no proprietary inclusions” makes it harder for a beginner than …
Ubuntu (and its derivatives, such as Mint) … Debian without the insistence on OSS, and with more polish, more help, more online resources … though as it’s used by a lot of beginners, you have to be careful where you get that help and vet it to a degree.
I’m Debian (based) all the way … but Ubuntu just take Debian and make it (arguably) better … certainly “easier” for a beginner.
That’s my 2 cents … for what it’s worth