This sort of question is very much a matter of opinion, but Linux Mint is a very friendly desktop choice. It's become my go-to for all of my desktop installs.

Honestly, in my opinion/my experience the best way to learn linux is to (1) just jump in and start using it and (2) being patient with yourself while you adjust. Nothing makes you quite as comfortable with using an operating system like using it every day, even if all you do is boot it up, open a web browser and watch gifs of cats on the Internet. When I was making the switch, it was invaluable to just be in there, using regularly. Second was also to be patient with myself. I found, at first, that i was getting frustrated when I needed to troubleshoot something because I was so used to the Windows way of things. I had to give myself time to learn and adapt.