I've used **** near all of them over the past 17 years of driving and owning a vehicle. Zymol is nice but it doesn't last long. Zaino is excellent but expensive as hell. The one that I have been using for the past year and a half (a world record for me) is none other than Cherry Wet.
You order it straight from http://www.coatsproducts.com and it comes in a gallon jug for $25 or so. I finally got smart and asked a pro-detailer who preps cars for car shows and for the local snooty dealerships and he put me onto Coats.
The stuff is so similar to Zaino that it's ridiculous and the results are outstanding.