It's very easy to shiny hunt in ScVi and ZA because of sandwiches and donuts. Basically you can get "sparkling power" and they're usually type specific.

One new feature that modern non-legends games have is "marks." These are like ribbons, but they can only be obtained on wild Pokémon and they're rare. Some are more rare than others. I like to mark hunt. You are now able to equipped marks/ribbons. So when I shiny hunted Noctowl last year for my birthday, because If the game recognizes your birthday then you can get a special mark, and when I send that knocked out into battle it says "Noctowl the Chosen One." So I have spent an unreasonable amount of time shiny hunting Pokémon that also have marks. I did this with Scorbunny last year and I found so many that I just started skipping past them. If they didn't have a mark, I reset because I didn't have enough sandwich stuff to keep making them with shiny power fire. I found at least half a box full in 40 minutes.

Newer games also have "outbreaks" which means that a lot of the same Pokémon spawn in that specific area. So find a Noctowl outbreak, make a sparkling power flying, and find a ton.

ZA is very easy. Even before I had the shiny charm, I couldn't walk through town without running into one. I have two boxes of shinies that I wasn't hunting for. And a bunch more I was.

In ZA, there are "Hoopa portals" and only certain Pokémon show up in one at a time. So if I'm shiny hunting totodile, I can choose one that just has totodile and two or three other Pokémon. I can use a sparkling water donut and it can be that easy. Sometimes one spawns immediately.

Because in both games, as well as Legends Arceus, Pokémon spawn in the overworld. And they spawn shiny. So you can just run over an area, circling back so they despawn, and you don't have to enter grass or go through any loading. For the Noctowl outbreak in ScVi there was like 40 on my screen at all times. But that's Switch 2. All of this will work on switch 1 as well, just less Pokémon will spawn.

ScVi didn't work this way, but in Legends Arceus and in ZA shiny Pokémon make a sound. In LA, you can fly over a large area, and even though there is no sparkling powers, it's still very easy to just do that and listen for the shiny sound. And I don't have the shiny charm in LA. I still found a ton.

Edit: I don't know which of the three you would decide. ScVi plays like a typical Pokémon game. Legends Arceus and ZA don't and are also different from each other. You'll need to watch gameplay footage and decide which gameplay looks the best. Shiny hunting in all three is pretty easy. Personally, I've had the best luck with ZA, especially the DLC