I have done both upgrade and clean install. No issue either way, but as always, it depends.... I would say unless you have overriding reasons, go with clean install.
Win10, in my opinion is an excellent version. I like it better than Apple's. I have win10 running on 1 desktop and 3 laptops, one of them is a MacBook pro (dual boot). On the MacBook pro I mostly boot to win10 as I find it easier to use overall.