Junior captain at BOS is a Jan '17 hire. But the CA at the 75% mark there is a 1990 hire. Junior captain at LGA is a Feb '22 hire. And the captain at 60% base seniority is a Nov '16 hire. So you'd undoubtedly have way more seniority early on at LGA. But most of the more junior CAs at LGA commute while reserves seems to go more senior in BOS. So your QOL will be highly dependent on your personal situation, but here's some data for you.