What I think you don’t understand is that there is no objective way to measure and evaluate what style is best in any particular approach. Different people relate to the material and the methodology in different ways, which means that a method that would be an excellent choice for you, could be a terrible choice for me.
Boxing can certainly deliver impressive results in punching; no argument from me. It is a popular sport and so gets a lot of visibility. This leads people in a general sort of way to assume it is the best possible way to develop your punches. But again, it only is the best for you if you relate well to the method and find it interesting and enjoy training it and wish to do so more than any other method.
What it means to develop the best punching is a subjective notion. Is it the most powerful? The quickest? The most “useful” (another very subjective evaluation in itself) combinations? Punching in combination with kicks or sweeps or takedowns? Everyone will have their own notion of what it means to be the “best” puncher. You will find no uniform agreement on that.
It seems to me that when one makes a statement that this or that method is the best, it is usually based on what his own personal experiences are. A person has trained a method, or even several, he found one to be very effective for him and so decide that one is the best, across the board. But how many other systems are out there that he has never trained? Thousands? How can he decide one is the best, when he has never experienced most of them, by far?
@Buka hit a solid notion when he said boxing produces consistently good punchers. No argument from me there. Boxing has figured out a method that produces solid punching in a reasonably short period of time so that an athlete can become an active competitor without needing to train for years on end first. A competitive career in boxing does not last terribly long for most people, so they need to get going while they are young and in their prime. So the methods of boxing work very well in the context of what is needed for that sport. And simply on an objective level, yes it can produce excellent punchers.
Circling back to your question above, what do I think is better? As I outlined above, my answer will depend on my personal experiences. I admit, I’ve never studied boxing. I am disinterested in it and will never do it. I study Tibetan white crane, so of course I feel it is better. Remember what I said in the above: people will make that evaluation based on their own experiences. I am no different. I feel Tibetan crane has an excellent methodology for developing very powerful punches in a surprising variety, and I feel it is second to none. If you have never studied Tibetan crane, then how would you even dispute my claim? But my claim is really just limited to me. Tibetan crane is an unusual method; it does not appeal to everyone, and is not widely practiced. I am ok with that, it does not bother me. I only make claims for myself, not trying to broadly apply my experiences to everyone.