Let's do some math (which I hope is correct):

In NK, our base commerce is currently 38, which creates 38 Gold. With a Bank, we would generate +50%, so we would generate 57 Gold. With a Marketplace, we would generate 47.5 and could run 2 Merchants producing 3 Gold each for a total of 53.5 Gold, at 0% Science. The Bank would free up citizens to be Scientists, so we could also gain +12 beakers per turn running 2 Scientist. Seems Bank is better here?
In Atlanta, base commerce is 20, so a Bank would mean 30 Gold. A Marketplace would give us +25 and with 2 Merchants, +31. The Merchants also give us +3 beakers per turn, so this city may do better with a Marketplace? Seattle is in the same boat with Atalanta, +20 base commerce.
edit - Congrats to Htadus for his Bronze in wotm39.