I had a dual boot with W7 and XP, I put my working W7 on the XP partition and did a clean install of 10 and rebuilt my system afresh as my main partition has been in action for quite a few years and originated as an XP installation that got upgraded so I figured on making a new start and dropping some of the things I don't use into the bargain.
Having imaged it I did upgrade it first though and that went fine and the lappy upgraded fine too.
So two upgrade installs and a clean one without any issues at all, no problems with hardware drivers or any of the software I'm using (Sonar 8.5 loves it!). The missus did hers too without incident during or since.
W10 seems a few Gb leaner (in terms of hard drive real estate) than earlier versions too but that might be to do with the amount of moss I gathered on the old system over the years. I've got W10 and the original W7 installs side by side now on the dual boot and XP is officially dead although I can still resurrect it at a moments notice if I ever feel masochistic or nostalgic.
The most painless OS upgrade ever, even given that I was lucky enough not to bother with Vista or W8.