Channel knife tips come in two shapes. Some of them are U shaped, while others are V-shaped. The V shape is classic and more common. While the U shape is relatively new, it seems to be more popular among buyers.
At the end of the day, it makes no difference in terms of efficiency. While the V shape will penetrate foods better, a sharp U shape can be just as efficient. The bottom line, choosing the right shape is a matter of personal preferences only.