(37mm RO) 15450st vs 15550st

Hey all. Planning on getting my first AP and narrowed it down to one of these two 37mm models. From what I understand, aestheticly these two are very similar, just with slightly different dials and case thickness. I assume the older reference has a more durable/water resistant movement due to the screw down crown.

Are there any other differences I should note? Does one wear better than the other on smaller wrists?