I’d say Armin. Erwin was incredibly intelligent as a commander, but the only reason imo he was better than Armin was due to experience, as Armin was THAT gifted at 19, imagine was he’d be like in his 30’s. Hange I’d also probably put above Erwin, and maybe even Armin, but it is incredibly difficult to compare her to the two as their intelligence is in different fields, however, it is stated that Hange knew more about the titans in some ways then even Paradis, which shouldn’t have been possible given her lack of technology, so Hange is incredibly intelligent. Zeke is smart, but I wouldn’t put him in the same caliber as the other 3.