I say Hinata.
It's not so much a battle between sight and smell, but rather whose tracking skills are more developed. If I needed to track someone down, I would choose Hinata over Kiba. She can see up to 10 kilometers (about 6.3 miles). Not only that, but she can see at least 6 miles in all directions at once (with the exception of the blind spot). Her ability to see through anything puts her ahead of Kiba's ability to smell.
As shown through rain, Kiba loses his tracking skills almost completely. Who's to say other smells wouldn't interfere with his scent? If a ninja created a clever diversion, he wouldn't know. Want to throw off Kiba? Take off your clothes :| and put them on a traveling animal.
In the shinobi world of tracking, you want to have as few shortcomings as possible.
Smell is, obviously, blind. Hinata can see what her enemies are doing exactly.
Why not Shino? His bugs may be more agile, faster, and more sensing, but he always seems to wait for them. He's a great tracker, but I see his clan's speciality as more poisons/paralysis/stuns. Basically, Shino is a disabler.
Just my two cents.
