Bear guns are guns that have penetration enough to break big bones and penetrate deep. The "best' bear gun is one that does these things that you can shoot well and fast.
I was the CEO of Cast Performance Bullet Co for some time and I have a LOT of experience with what works, what doesn't and so on, but I can tell you faithfully that a good 357 Magnum with hard cast LBT Bullet or heavy Keith SWCs is FAR better than a 500 S&W, if you can shoot the 357 better and faster then the 500.
We have a tendency to look at guns when we should be looking at shooters.
If you develop the skills to use the heavier more powerful guns then they are better.
More is better, when loosing the fight means getting permanently hurt or killed, but what's going to save you is accurate hits, and because of that I recommend using the most powerful gun you can shoot well.
Let me repeat "that you can shoot well."