I would have to say neji and lee. Kakashi is very fast, intelligent, and has the sharingan which grants him with predicting capabilities and a large arsenal of jutsu, including the mangekyo, but neji and lee both have great speed and very formidable techniques.
Neji alone is a master of the byakugan and the gentle fist and is also considered to be a genius himself by his own rights. He has powerful eight trigrams attacks and defences such as 64 palms and rotation.
Lee on the other hand is a master of the strong fist and is one of the fastest shinobi in konoha whose speed, stamina, and technique is so great that it was worthy of imitation by both naruto and sasuke who are both very powerful shinobi. He has the eight gates to use which can put him on par with a kage.
It would be close, but neji and lee would most likely win this one