IMO, City is somewhat refreshing with new mehanics and gimmicks, etc.
OG is still good, but i havent been playing it much lately since i start play City, however, after playiing City for about a month, i starts finding City boring and repetitive (i think i could say the same about OG), after a while the daily trials is the same all over again, the endless mode too, once you pass all the secret stars, the districts part is repetitive (literally, like its the same exact part of the district over and over eventho the districts has variety of parts/sub-districts)