Ren'py, would be the harder one, I believe.
As far as I am aware of, Ren'py is all but coding, and at most you can get code from others to use in your project, thus people may joke about it but animated scenes with layered clothing very likely is not easily done in it. Although I admit not going deep into how it works.
I am perfectly aware of what base Unity works, as I used it for my university. It has a visual part to it, including able to visualize animations running as you make the game, and many external plugins to make the job easier - one of them, the one Gunsmoke is using.
I don't really get the second part, but I am guessing that you mean "using the experience they already got from up to now, how easily could they adapt to an engine trade"?
With the above in mind, I would guess the one with experience in the more code-heavy one.