Neji with extremely high difficulty. Chakra destroys chakra, as Neji shown us from his fight against Kidomaru. So even if Gaara trapped Neji in sand, just releasing chakra from his body should get the sand off him. But Neji would have to try to hit Gaara's tenketsu through his sand armor, which is possible, but extremely difficult. Once that happens, any hit from Neji should hurt Gaara's internal organs. Technically, Jyuuken forms of attack is better than 64 Palms. Just one hit to Gaara's heart will damage him greatly, so long it goes through the sand armor, which I think it could.
Gaara is a stationary fighter, so he either shields himself or fights from a distance. He really has no strategies involved. Neji on the other hand, is a seasoned taijutsu fighter, along with Jyuuken and Byakugan. I think Neji can take it.