Curious Village for sure. That game oozes with charm in a way that none of the other ones managed to match (in my personal opinion). I bet you'd be able to get it for dirt cheap now too.
But honestly, it probably doesn't matter. There's a little bit of continuation in the story, but you won't be lost if you jump in at the later ones. If Miracle Mask is the one you can get most easily, then get that one, and pick up the rest later