>>51174181I agree that they aren't fit for a first timer who wants to experience the games for the first time, buuuuuuut, regarding Polished, you can disable all of the Natures and Type changes from the options menu. And also it's getting an update real soon that re-adds all of the cut mons. along with a bunch of QoL improvements including a vastly improved Box (picrel).
So my advice would be to play vanilla Crystal, and then if you really enjoyed it and want more (because it's pretty easy and you can't complete the dex without trading anyway), I would recommend going through Polished Crystal as a New Game+ / Master Quest of the original game. (I'm a big Polished fanboy.)
Crystal has held up pretty well in my opinion and doesn't need mods to be enjoyable. If I had any hacking know-how, I'd make a Crystal hack that added Running Shoes, runs at 60 fps instead of 30, and has all mons catchable on one cart. But I do not.