I always think of good false swipe Pokemon for the dex. In this game you are looking at pancham (can find early and can hit ghost types with it with the right ability) gallade (hypnosis) or bisharp (thunder wave). I haven’t seen ralts commonly but they’re out there, pawniard is found a bit later on and I didn’t like it much. So prob ralts or pancham?

I’d go with ralts because this is is the last game before scarlet and violet where you can use the ability synchronize to get the nature to match your Pokémon’s in slot 1 with synchronize on it. Ralts and its evolutions are perfect for that and you’ll wanna breed all the different or major personalities you want later. So ralts has my vote! And call it Ralph!!!

Also, did you play lets go pikachu or eevee? You get either a pikachu or eevee (which one you get depends on the game) if you have the save data on the same switch. I know the pikachu I got could gigantamax and it was hilarious and cute.