Re: what is thr easyest??
A lot of games that use the Powered by the Apocalypse [PbtA] engine are pretty easy to pick up.
Grab a playbook, create a character by making a selection or two.
Most games have 4 or 5 basic moves that everyone can do and then each individual playbook usually adds something thematic and unique.
The basic moves could be explained on a single sheet of paper.
The dice mechanic PbtA relies on is 2d6+attribute, and there are only three results [-6, 7-9, and 10+]
With this post and the info contained in plain english on a character's playbook ... your players would be ready to begin.
It should be said though that not all PbtA games are created equal. Some are very good for beginners and some of them decided to add more complicated mechanics [the complicated games might in and of themselves be fine, but they might not be a good place to start].