I've been reading this thread and am going to add my 2 cents.
There was a time that I used to build my own pcs, install windows, etc. etc. etc.
I guess I've just gotten too old.....or they started changing things faster than I could keep up with. So my son, who lives and breathes IT now does all I need done when I can get his time.
Anyway, here's my story on 7 and 10.
I went on 10 a bit before Thanksgiving and all in all it's been fine. We first did a 10 upgrade and about 99% of things worked. The one thing that did bite me was I lost and could not install a working driver for my HP9800 (even though there was one before the upgrade) rendering it useless unless i swapped drives to boot up on a backup copy.
The reason I was not wild about a fresh install was the usual PITA to reinstall all my software and applications. Anyway, this last weekend, I got a new fresh SSD drive (we only use SSDs of about 80 Gigs since nothing but programs and Win is essentially on it and they are really affordable in that size) and my son installed a fresh copy of 10 and it works fine. It automatically installed drivers for the HP9800, which the upgrade would not even let him download new drivers from HP. HP9800 prints fine now.
What we found was that you could download a latest copy of 10 and roll forward where it recognized the exiting 7 and installed. No key entry asked for. You can also start fresh and install a new version of 10 on a new drive using a 7 key, which someone mentioned above. In our case, however, on the first go-around, the upgrade to 10 posted a registration somewhere on a MS server so that doing the fresh install, with the original upgrade drive sitting out on the desk, 10 installed and the MS server recognized that we had already installed and knew the registration so it went right on through and automatically re-registered.
My son says, notice it's not me, that as long as users are happy with 7, or 8 and apply the updates, MS is still supporting so should not have any issues with vulnerabilities.
According to my son, MS optimized Win 10 and it runs much better using less hardware and resources.
For now, I have to say 10 is up and running and is working fine.
The IE browser was replaced by MS Edge, but you can still get a normal IE loaded if you like the feel better than Edge. I have both on the task bar and actually use the original IE for logging in remotely to work. For normal surfing I use Firefox.
