It depends on your physical conditioning and build. Again depending on your body, 40-45# is generally a good starting weight. Go less if you need to. But as you get stronger move up to a higher weight. Don't stop at 50# because it's a popular weight. Now, if that is what your body tells you, LISTEN. The higher weights improve trajectory and penetration.
I prefer 65# especially if you are talking animals up to elk. Can less get the job done on any animal in North America? Absolutely. By some standards 65# is considered heavy weight, but I can draw it easily, hold at full draw, and shoot accurately. I have no reason to want to shoot a lighter weight and I get all the benefits of the heavier weight. Everyone has limits based on their body and amount of conditioning/shooting they can do. When I shoot 80#, the weight makes it more difficult to focus on the fundamentals of executing a good shot. That currently makes it a bad choice for hunting for me, so I shoot it more for conditioning.
Listen to your body and gradually work up to your max. In that process you will find a weight along the way that is best for you. It might be 40# but it may also be 70#. But a controlled 70# is far better than a controlled 40# for hunting big game.
Just make sure you don't lose control of the fundamentals in an attempt to shoot a higher weight.
Remember that arrows are slow projectiles which require precise placement in order to kill consistently. Bow weight, tuned arrows, and sharp broadheads become really important when something went wrong and arrow placement wasn't precise.