It’s a difficult one, because the other teams all struggle when Kane, Lukaku, or Salah have a lean spell.
City look faster, and certainly create more chances without Aguero. In fact I’d suggest that the quality and volume of goals from Sterling, Sane, and Jesus, has probably contributed to City dominating the Premier League more than any other factor.
However, in a one-off game, when your whole progress depends on clinical precision, it would be Aguero over Sterling every time.
Whether Sterling can keep improving is debatable. He can develop his technique, but some of it seems to be in his head,