The way I understand it the difference in accuracy between a 24" or 26" barrel would be minimal, IF there is any inherent difference. Both can potentially be accurate but the difference is more likely to be due to other factors, such as quality of materials and manufacturing tolerances, rather than the length.
Logic seems to indicate that, given the same contour, a shorter barrel will be stiffer, but even that doesn't necessarily mean more accurate. I think there are too many other factors for a generalisation like that.
If every fps counts then a longer barrel will deliver higher muzzle velocity (up to a point), and that's more likely the governing factor. That and the practicality of carrying around a longer barrel.