Clean install all the way for me, I don't want no crap left behind by upgrading, windows.old etc, I know it can be removed etc but I personally prefer it to be from a fresh install.
I fail to see the extra hassle part of it though, it's simple enough to keep your data on a separate drive and just use a SSD or similar as a boot drive for Windows. That's how I do it anyhow.
For me it's the other way round it's more hassle having a upgrade over a clean install because of the issues I stated, that's a good enough reward for me. I do understand however some users are not that technically minded and just want their programs and data the way it was before upgrading, all depends on the end user.