Windows 10

https://www.grc.com/never10.htm

In the meanwhilst, have a play with Linux Mint (Mate edition).

You don't say what hardware you have,
but if you have a spare hard disk, do it on that, dual boot will just confuse you.
Another option is to buy a modest SSD for a hundred bucks
and put it on there for some fairly vivid boot times.
Either way, you will need to lock in your "free" upgrade SOON
or end up paying later. This is a work around.

http://www.zdnet.com/article/how-to-lock-in-your-free-windows-10-upgrade-and-keep-using-your-old-windows-version/?tag=nl.e539&s_cid=e539&ttag=e539&ftag=TRE17cfd61