Debian it is. I've read about Debian and it sounds good and easy to install. It also sounds like it's targeted at new Linux users, people coming from Mac and Windows. I'll try it as soon as I have access to my full selection of Macs again.
No, Debian is not an entry level distro like Ubuntu/Lubuntu etc - it's not rocket science but it does require a bit of work to become fully functional.
It's great if you want to start with an absolute minimal system and only install what you need.
No current Linux distro will beat OSX for speed - if you want that you need to dig into the archives and get an older release.
Not that I'm knocking Linux - I've tried it many times but always come back to OSX because it suits my needs.
Lubuntu 16.04 worked really well on my 12" Powerbook - however, CPU use was pretty high all the time.