@BrerJon already answered and I agree. If you are talking now - definitely Tokyo. 2017/2018 Paris will have finished its refurbs and will be celebrating the 25th, so might be worth delaying Tokyo for the 2020 Fantasyland revamp to come online at that point in time.
Again, all depends on if you are talking about planning a trip for two years in the future and a few years after that, or feasibly are hoping to do both within the next few years.
Of course, if the scenario was only doing one - Tokyo, a million times over. Well before Shanghai, Hong Kong or Paris.