I started with my main PC - an i5 with 16g of RAM. Hand built box with a newer nVidia graphics card. I upgraded from Windows 7 to Windows 10. Had to find one off drivers from my sound card but got that working.
Then I made the mistake of using the MS website to order an Xbox One for my sons for Christmas. MS switched my login to use that account. I did NOT want that to happen. Then my network card got confused and it could not see the internet so I could not log in. After many hours of screwing around with way too many tools I finally was able to create a different admin account, get the network working again and then log back into my main account with the MS website password. I was hating Windows 10 at this point and I wasted way too many hours.
I got my sons machine, that was on Windows 8.1, upgraded next. Another pain. Everything was working until yesterday. This is also a hand built machine. Now I just get a black screen with the basic white mouse cursor running about. Tried for a couple of hours yesterday to get that resolved but no such luck. Might have to reinstall I don't know.
My wife's parents installed Windows 10 on their box and then lost the ability to talk to their Android phone and Kodak camera. This is a refurbished eMachine from Microcenter. I was able to get things back up and running by doing some manual driver installs. Still don't trust everything but it is working for now. Also a Windows 7 upgrade that was an upgrade from Vista. The main menu was broken on this machine until I uninstalled drop box and reinstalled it. Took hours to figure that out as well.
Looked up my wife's Lenovo laptop and it is recommended that you DO NOT upgrade this box as you will lose sound. They just are not going to do drivers for it. Since I have had all the other issues really wanted to skip this box too.
A friend upgraded her newer Lenovo laptop to Windows 10 and then brought it to me as it was all screwed up. I upgraded every thing I could on the machine, mainly Lenovo drivers, and got it back in shape. Since then it has been working OK for her, fingers crossed.
Not doing either of my son's laptops. Older laptops and he attends a virtual school so having them down would be a huge hassle. They will be left alone until they die. Both on Windows 7 at this time and they run just fine using that.
Finally I am skipping the family file / print server. Windows 7 on another refurbished eMachine. Just as stated it is file / printer server that does M-W-F backups to an external HD. Everyone stores everything out there so you can use any machine in the house to get to things. It also needs to be running at all times. Not going to risk Win 10 screwing that up.
I just can't recommend Win 10 as an existing machine upgrade. Yes, once I got it going on my main PC it has been fine. I do think MS is being way to snoopy with this update as well. I disabled all the call home stuff I could on all the machines that I did upgrade. But I keep running in to new issues. Have to get my son's machine out of black screen of cursor only mode. Did the boot from physical media and tried to get it to repair things but no luck there yet even. Lots of posts about this issue, some get it fixed, others do not.
You will have something broken. It will take you hours to figure it out. You will cuss and scream at all of this. Sure Win 10 is fine on a new machine but upgrading has been very painful and I now I have a machine that is down again. Plan on cussing at it tonight some more trying to get it back to life. I will not risk any more machines in my house and I have warned all family and close friends to not update and just to ride out Windows 7 until they get a new machine.