What is the best upper chest exercise you ask? There is no such thing. Over the years I found out that upper chest development depends more on genetics than a particular exercise and while incline presses are great they can't beat genetics. With that being said I still believe that the incline bench press, reverse bench press and ring push-ups are one of the best possible exercises for upper chest but exercises like dips will also bring your upper chest if you work hard at them because a muscle is a muscle and while you can emphasis a certain part of it, depending on the angle, in the end of the day it works as one whole unit.
You are probably wondering why the reverse bench press? I don't know but many people swear by it. Also another exercise that is recommended are pec minor dips. You can use smith machine for the reverse bench press - no need to go all functional strength on this one.
Give those exercises a try - you have nothing to lose.