Back when ArmorAll was "the" thing to use for uv-protection of rubber, vinyl, and such . . . I asked that same question from people who had nice looking OEM vinyl tops. Many said "soap and water ONLY", which sounded a little unusual to me. Kind of like just washing your car and not waxing it.
Some "protectors" will put a shiny sheen to the vinyl, which doesn't look "right" to me. I ended up using STP "Son of a Gun" on my '67 Newport when I got it in '81. It has continued to lead a somewhat sheltered life and the top is still there, OEM. I used a sponge to apply it, rather than a rag, which just seemed to work better and get a more even thin coat of it on the top. DO let it sit on the top for a while before you buff it off (another sponge, then a lintless bath towel, which seemed to work best for me). Then wait a few more days before any water gets on it . . . OR the "streaked windows syndrome" will occur. After it gets some age on it, you might park the car inside to do the application and "cure", maybe doing it twice for good measure before you let it cure outside in the sun for its final exposure after the protectant.
The reason I ended up with the SOG product was that it left a natural sheen to the vinyl, rather than an artificial shine (that was not natural).
Enjoy!
CBODY67