What to protect Jeep soft top with?

Hey guys, this week I'm detailing a Jeep wrangler with a soft top that the owner is trying to sell. He went off roading in it a lot and almost never cleaned it. After I spend a while cleaning the soft top what should I protect it with? The two products I have on hand that I was thinking about are 303 and UTTG. What do you guys think? Thanks!