I don't think there is one "best way."
Different approaches reach different people, so the more good stuff that's out there, the better.
That said, it takes great patience to overcome WT indoctrination.
I don't think mailings are effective -- too easy to toss them away as apostate literature, turn them over to the elders, etc.
Going to the KH to "plant doubts" is likewise risky. You have to be very subtle or you'll only stir up opposition and get banned. If you keep coming back after that, you could even get arrested. It's happened.
Whatever you try, do your best not to trigger the WT stereotypes about apostates, demonism, us v. them, etc. That's usually counterproductive. It usually just drives JWs back to "mother" (the organization) for "protection."