As I'm sure you're well aware my BIL has flown both 737-800's and A320's. I asked him his opinon about the 737(with all due respect, the 737NG is NOT a 757!). He prefers the 737-800.
Rode a A320 jumpseat this past weekend. Loved the size, view, and quietness vs. the 737. I wouldn't bothter switching aircraft to get A320 qual'd but IMO the cockpit is worth it if everything else(relative seniority, trip quality) is the same.
Now if Boeing comes out with the 797 in 2019-2020 as speculated, that, IMO, would probably be worth the wait.