Before the time-skip, it's Neji. Kakashi states that Neji is way out of Sasuke's league at the Chuunin exam.
After the time-skip, let's say before Sasuke fights Itachi. Sasuke has an unblockable attack in the form of Kirin, so even Neji's rotation technique is not fast enough. Also Sasuke knows about the Byakuugan and can be a long range fighter. I want Neji to win because I think he's cooler, but if Sasuke can avoid Taijutsu and close-combat, I give the nod to him. The other factor is that I think Neji expends more chakra defending attacks like Sasuke's than Sasuke does composing them. For example, defending against the fireball jutsu, if Neji can't dodge it, I think he has to use rotation, which is chakra intensive.
Honestly, I haven't seen enough of Neji compared to Sasuke to make a fair comparison, but Sasuke is a main character, so that's the way things go.