Whoever wins this will win with high difficulty no question.
While Sai is more of a long range fighter which has an edge over close range, I am slightly edging moreso towards Neji due to his byakugan. He will be able to see and counter everything that sai wouild throw at him since he uses mostly ninjutsu. Neji is also very quick being with team guy and has some ranged jutsu, such as air palm.