I have used 303. I find Vinylex to be superior. Go to www.carcareonline.com and read all the how-to articles. That fellow carries most of the brands, will sell you whatever you like, but is honest about his opinion. He is the reason I tried Vinylex and I continue to buy it, although, now at Pep Boys. The other items I buy from him.
I have big bottles of both 303 and Vinylex. The 303 bottle is still almost full, the Vinylex has been replaced multiple times.