It will largely depend on what type of terrain you will be riding and on your body profile. The larger the wheel sizes the harder to maneuver the bike through rigid or twisted trails. Though 26” is the most popular wheel size most MTB riders like it to be not less than 27.5”. Our personal suggestion would be 29” for the smaller riders, but if you are going to use it on muddy or rocky terrains then opting for 27.5” would be wiser. Wheels less than 27.5” provides better maneuvering on rigid and tricky terrains but the comfort is less.