In a city campaign I feel that you could end up with very short adventuring days often - not always, but more often than other styles of play. Also there seems like there would be a lot of cases for doing "other" types of challenges outside combat. As such I'd recommend D&D 4e. I'll make no bones that in general I prefer 5e over 4e, but inter-class balance is not affected by the length of the adventuring day, and the concept of Skill Challenges I feel is very useful, doubly so in city adventures. (Though the math on it was wonky and could use updating, plus the inclusion of other types of limited resources.)