I started up with Zep since I knew their products and was able to order by phone. Didn't like their chamois or their greasy plastic dressing, but I like their APC, Alum cleaner, brushes, enzyme deoderizers (don't like the smells) and most what I've used. I use their foam shampoo for light to moderate dirty cars, but nothing special about their glass cleaner.
I've also moved on to a local supplier (my cousin), but I'm still testing a lot.