It probably depends a lot on whether you count cities with non-partisan mayors. In those cities, I'd say that "Republicans" have an advantage, but I doubt there's any data on that. In cities with partisan mayors, I'm guessing there's more Democrats.
I think now it's probably the opposite. Starting last year, I noticed Republicans were much more likely to win when it's a partisan election.
That may be true, but I'm assuming that elections are more likely to be partisan in bigger cities, which are more likely to elect Democrats.
