We'll start with the most powerful suit he's ever piloted, the Epyon. Built by Treize and equipped with a Zero system and heatrod, this crimson beauty is second to none.
Next, we have Zechs' first above average suit, the white wonder Tallgeese. This prototype Leo is so strong, large, and puts so much pressure upon the pilot, that it was deemed unnecessary for the military's uses, and was discontinued. However, our favorite rebel prince somehow -- with the help of loyal Lt. Walker -- got his hands on one, and mastered it.
Moving along, there's the Tallgeese III, an upgraded version of Tallgeeses I and II. As far as I can tell, III has simply been modified somewhat, scaled up to compete with the customized Gundams, given more defensive armor and a heatrod.
Last but certainly not least, there's the Wing Zero. Although it was only flown and fought in once by Zechs, it still classifies as having indeed been piloted by him. This powerful Gundam can only be challenged by the Epyon itself, as it is the only other mobile suit in existence to have the Zero system.
