It really depends on the broad context, I think. All of them can either job or be somewhat overpowered, based on the situation. I'd say that Garnet is probably the most reliable over all, but I'm not sure if I'd call her the weakest. Starfire is more strong, but if we're using the Go version all of the characters are intentionally comedically unreliable. Then there's Nicole, who often changes from defeated parent to God mode in seconds. In a "serious" fight, I think Starfire would probably win, but I guess it's up to whoever's writing it.
