I like PwC. It has better cleaning ability than VM and is more durable. I haven't tried my sample of Pro Buff yet, so I can't offer an opinion there. For over the counter stuff, I really like Mother's Carnauba Cleaner Wax.
Megs #20. Cleans well, leaves a great shine, it is a polymer sealant and very durable. Easy to use to, wipe on let haze and wipe off. Great for wheels, door and trunk jams, and under the hood.:up
#20 is actually a very good cleaner. I found this out when I used it on the wheels. Removed some stuff the wash didn't and turned my applicator brown. But yeah the cleaners are not as strong as AIO or a similar product.
#66 is what I've been using for a while as it's cheap and comes in a gallon size. Generally apply with a polish pad/pc. Did a vehicle about a month ago and after 2 washes it's still pretty slick...
PwC is Poorboys polish with carnauba. You can find it at autogeek.net, specialtymotoring.com, or poorboysworld.com. As for whats the best one step I think I just read something from one of the new posts here that vanilla moose is a good one step.
AIO is a good cleaner, but it's longevity is a bit of a question mark, since most people top it with SG or something else. I know I never use AIO alone.