Choose a 240mm gyuto if you need longer reach for slicing large cuts of meat or working on big cutting boards, but opt for a 210mm gyuto if you prioritize maneuverability and have limited counter space.
The 240mm length offers a longer cutting stroke, which is useful for slicing through large roasts or fish whole, while the 210mm size provides better control for detailed work and fits more easily in standard home kitchens. For a concrete example of the larger option, the Yoshimi Kato Hyo SG2 Gyuto 240mm is available for $600 and uses SG2 steel. If you prefer the smaller size, the Masakage Yuki White2 Gyuto 210mm Stainless Clad is in stock for $460, or the Hatsukokoro Kurokaze White 2 Gyuto 210mm Stainless Clad with a Tall Profile is available for $300. The trade-off is strictly between the extra reach of the 240mm and the lighter handling of the 210mm; neither is objectively superior without knowing your specific board size and hand strength.