Pokemon Lets Go - its good, but some of the mechanics in game are kinda weird, so its not exactly faithful to the originals, but its nice way to re-experience them. Id put it at number 2.
Sword/Shield - This is my number 1. Its like a mix between the old 3DS games which i love, and their newer open world style (but on a smaller scale). My favorite of all the Switch games. Has the depth that you want from a Pokemon game - breeding, IV's, EV's, egg moves, all that, plays like how you expect a Pokemon game to play.
Legends Arceus - People love it but i think its meh, all open world, whole new mechanics, so its worth checking out. Just dont expect Breath of the Wild or Genshin Impact. This is more like, "babies first open world game". Game is grindy too, "Use self-destruct 50 times!", also looks pretty terrible. Pokemon are just placed in biomes, but they dont really do much of anything organic. Not immersive in the slightest. The world has nothing interesting going on to discover.
Scarlet/Violet - avoid. This is more, "babies first open world". The only things noteworthy or creative about this is how open world gyms work, doing them in the order you decide, the other thing is it has multiple main stories going at the same time, giving you plenty to do besides gyms. It runs like crap. Looks like crap. The character customization is even crap. Game has almost no imagination.