Many excellent points shared thus far by helpful people with significant moose hunting experience...
We hunters vary (perhaps greatly) in the accuracy potential of the rifles that each of us bring on the hunt, as well as the amount of practice hours we spend at the range to get to know that rifle and load, and enhance our shooting accuracy with that rifle. We vary in other ways as well, e.g., how far out we are willing to take a first shot, our patience when an animal is in our sights, etc.
All of that is my preface to reiterate what others have shared, i.e., the most likely (definitely largest) kill area on a bull moose is a broad-side shot in the lung/heart area, which I have done a number of times. The bull will die, and it many times dies standing right there not knowing what just happened until it falls over dead...sometimes it runs off and dies. Patiently waiting for a standing broad-side heart/lung shot at a distance you know you can hit reliably is your best/bet shot placement.
That said, I've been head/top of the spine shooting moose for the past ten years, and it works for me. I do that because I've been hunting in a predominately wet area for the past tent years, and I want to anchor that bull on the solid, dry ground where he is standing. I also like calling bulls up close to me (so my shot is most always well within a hundred yards...except last year), and I've used the same rifle for many, many years with the most accurate handloads that I developed. I did have one mishap a few years ago, when I wounded a bull who then ran and jumped into a nearby pond/lake...and died floating out in the middle. The whole thing was my fault because I did not check zero after transport. Fortunately we always have a self-made z-drag system with us, so we were able to get him up onto dry ground, butchered, bagged, and hanging by last light.
Edit: For clarification, when I reference "head/top of the spine" above, I mean shooting the bull in the head or the first few cervical vertebrae of the neck where the base of the skull ends and the neck begins.