While neither is going to impress at the dragstrip, It seems the Tundra holds a slight edge a quick Google search unearthed 6.0 seconds for the Tundra and 6.7 seconds for the Titan. A visit to the manufacturer websites unearthed a few more relevant figures. The Tundra makes 381hp and weighs about 5645 lbs. The Titan makes 317hp and weighs 5297 lbs. This means that each horsepower unit that the Titan produces must move an additional 2 lbs. This may not sound like much, but it is likely to have a significant impact on 0-60 times.
