>>36632147I haven't played all Gens but ouf of the ones I played: 7 > 3 > 5 > 2 > 1
Sun/Moon go first because 1) they are the best at making me feel like I'm 'playing' the anime and 2) they offer the most mechanics to create a bond with your pokemon (petting, healing and affinity system with battle benefits). Incidentally, this bond also has the positive side-effect of giving you bullshit MC powers (your pokemon scoring criticals because they want to be praised, or your pokemon shrugging off status ailments because they don't want you to worry).
Now, SM has problems such as being too railroaded, but the pros I described above outweight the cons for me.