To clean...Audi A4 because I drive one and could probably clean one in my sleep...but I hate to polish them because correcting Audi paint is a pain.
As far as before and after results. I LOVE to accept honda details. I've found that the factory paint is very soft and really not that nice at all...BUT that usually means that the car is all marred up and swirled and because the paint is pretty soft it's also pretty easy to correct. The before and after is usually the most shocking of any car brand that I've done yet.
Any classic. I enjoyed doing a 65 Mustang so much I only charged the guy $50 for 20+hrs worth of work. Before anybody jumps on me for giving away a detail he also agreed to do some advertising at car shows. The $200 I knocked off the price more than paid for itself. I've done a couple motorcycles and also like doing those.