When I bought my Titan I did a lot of research on plugs becasue like many here it seemed confusing. What I found out:
Double Platinum (platinum at both spark contact points) are recommended as they have a long life. You can run the single Platinum but plan to change out sooner. Iridium is used for extreme long life. If double Platinum gets you 100,000 miles, Iridium is supposed to get 150,000 miles.
If you never run E85, you can use the common Platinum/double Platinums in your FFV Titan. Apparently Nissan also specified a particular metal coating on the factory NGK plugs for FFV Titans as denoted by the "D" at the end of the plug code. I have not confirmed this but suspect it resists the corrosivity of the E85 a bit better.
As I have no problems changing out plugs sooner than later I recenlty put in the NGK single Platinum LFR5AGP with 0.44 gap with 60,000 miles on the engine. Stock PLFR5A-11D's had a slight bit of build up. New plugs really smoothed out the idle, driveability and improved throttle response. I would never wait till 100,000 miles to change out the factory double Platinums so running the less expensive single Platinum sis good enough for me.
This is the info I have come across. Do your homework before making your own decison (the caveate).