5w-30 is the recommended oil type for the Titan. Unless you have a very specific use don't deviate from that recommendation. Always consult your mechanic before choosing to deviate from the manufacturer's recommendation. With that being said, there are countless options available and virtually every store has a house brand.
So the question is, which oil type is the most popular for the Nissan Titan?
Mobile 1 Oil is the most popular choice for the Nissan Titan. Thousands of Titan owners have run this oil on their vehicle without experiencing any problems.
Specifically in the hotter areas of the U.S. such as the Southwest, engine temperature increases and overheating can be a serious problem.
Mobile 1 seems to be up to the challenge with very few owners ever experiencing overheating issues.
Realistically, any oil brand will serve your Nissan Titan well. The most important thing is that you continue to change the oil on a regular basis. In addition, pick a high quality oil filter that also is regularly changed. If you don't change the oil out based on the recommendations on the bottle, you'll experience issues quickly.
Other popular oil brands for the Nissan Titan are Royal Purple and Amsoil. Each have their own cult followings, with raving fans who wouldn't dare pick anything else.