I can attest to the devastating effect of a shotgun with 00 buckshot. When I was 13, my best friend was killed by a ****ing idiot showing off his new shotgun. He was shot from a distance equal to the length of a truck bed square in the chest by a ****ing idiot who forgot his weapon was loaded. His brother witnessed the entire thing and told me he was dead before he hit the ground. Heart and lungs were destroyed.
Deer run because they are often shot from a distance greater than 100 feet, they don't get the full effect of the all the pellets as they are beginning to slow down and scatter, and aren't taking those pellets center mass in the chest.
If I could only have one gun for everything, it would be a .357 with a 4 inch barrel. There are better weapons systems available for almost any scenario, but would not measure up to the .357 in others. Its point and shoot. No having to mess with a safety, chamber a round, cock it, etc.
If you are experienced, you may want the .357 auto version, a .40 glock, shotgun, AR 15, depends on your level of experience and comfort. But a choice of one gun for every situation and every experience level (assuming a basic level of competence handling a firearm), you won't go wrong with the .357.