for Me Ultra Sun And Moon Because It has the most pokemon available if you include all legendary and island scan pokemon and it has character customization, festival plaza (same as join avenue but better), addictive mini games(ex mantime surf,ultra worm hole,alola photo club),it has its own battle frontier if you combine(battle tree,battle agency,battle royal),post game story (team rainbow rocket) and battle gimmick(such as mega and z-moves) and also we don't have to deal HM into your pokemon moves

how about you which is the best?