I've been a Rain-X user for many years. Nothing beats it fresh, but it's fresh for about 36 hours, which counts for 18 in Hawaii.
I tried JetSeal 109 but it was so awful on glass that I chemically stripped it after a week because I couldn't deal with the haze and complete lack of hydrophobia. Works great on paint, though.
I found this at a kiosk in the mall (go ahead, laugh at me). I waited a few months before I bought anything from him, because I'm skeptical like that, but when I asked him what to do about windshields, since I'm not happy about Rain-X's ridiculous lack of endurance, he showed me this stuff:
The box was beat up, but he said his wife brought home a suitcase full last time she was in Japan.
I've only had it on for a week but it still works, which is amazing compared to Rain-X. Like, beautiful sheeting. The guy at the kiosk says it seems to last years, but we'll see. The bottle above cost me $15 and should be enough to treat at least 20 cars. I have no idea how to buy more so this probably doesn't help you at all, but wanted to share anyways, since I've never seen anything work so well, even after just a week.
Cheers,
John