If Sasuke can't use the seal, then the outcome of the fight should depend on the terrain. In an arena such as the one in the preliminary fights during the chuunin exam, Sasuke would probably win because, as has been said, there's just little that can be done against the sharingan in close up combat because it predicts the opponents moves. Now, in a setting like the forest, if neiji could do some long range combat, he would have the edge. With his byakugan he could keep track of Sasuke's movements and set traps or attack from a distance, or even get the jump on him. Sasuke would stand no chance in that kind of a fight.
My vote: Neiji.
Why? Because I think Neiji stands more of a chance against Sasuke in an arena battle than Sasuke does against Neiji in a forest battle. if Neiji were to use something like that mist jutsu to limit Sasuke's vision, and then use his byakugan to find and keep tabs on Sasuke, then Neiji would have essentially succeeded in transforming the terrain to one that contained some of the advantage of a forest.