I like Renpy the most. If it`s a good game i tolerate RPGM.
With Renpy I can mod the script files. I hate missing scenes if it isn't important to the story. I want to see all in one playthrough if possible.
With RPGM i just use MV Cheat Menu if needed
Depending heavily on the game and how the actual story is (yes, plot can be more than just boobs):
-RenPy works on most cases (sandbox without any content is another pit)
-RPGM can be tedious with running around map for 10 minutes to see one scene and then back gain. (and those filler battles)
-Unity if coded well, pretty good games there too
-Unreal... well.. hit or miss IMO.
i think unity is overkill for these types of games, most of the devs are bad and then the games feel sluggish. i think renpy is just good for vns overall.
I prefer renpy games myself. Sandbox is ok sometimes, but when it introduces too much grind it sucks. Lets be honest we all play these games for a reason, and it's not trying to get stats, but something else, up.
As a consumer and a sucker for sandbox games I really like Faerins games, like Man of the House, which uses Unity. It feels like a fully fledged, big production game.
Don't really care. If the developer is good, he can use anything. But most of them aren't, so there are the VN-s in unity, without skipping or VN-s made in rpgmaker. These are not really my cup of tea.
But ultimately it is the story and the girls, if that is good I can play with any inconveniences.
I prefer renpy games, they just work on different os and are nice and simple. My second choice would be some html games. I believe Twine is the framework they use.