Most versatile handgun, shotgun and long gun?

Interesting question. I think in general for versatility you would want a large caliber gun. In general, a large caliber can take both large and small game, whereas a small caliber gun would be more limited to small game. Of course, there are exceptions and there's the damage to the meat of small game, but I think your .44 Mag and 12 gauge choice are examples of this theory. Applying the same thinking to rifles, I would think something like a .30-06 would be a good choice.