Some'a the other guys have their favorites but I don't think you can buy a better vinyl protectant than 303. You can use it on your windshield too btw. That's actually what it was designed for. Then somebody discovered it worked as well on vinyl.
Fyi 303 Products was recently acquired by Eagle One. Makers of Sta-Bil, Nev-R-Dull, etc. Dunno if'n that's good or bad, yet.