I don't believe there has ever been any question as to the "effectiveness" of a 12 gauge. And it's still one of the "most feared" general purpose weapons available, as they turn targets into
hamburger meat. You will find that #4 shot has the "best" overall performance for spraying a lethal dose of lead at medium range and closer.
DO NOT use slugs for HD,... EVER. Not only will you have to aim it, but the penetration may pass all the way through your home,
oblitterating everything in its path.
The downside to most shotguns would be, that it's still a long gun. Thus making it a little more difficult manipulate in certain circumstances. That's where short barrels come in handy as well as the pistol grip. My personal favorite load is #4
LOW RECOIL ammo by Winchester. It offers excellent knock-down blast while keeping the shotgun in full control for follow-up shots if needed. Mossberg is a good choice for money. However, there are lots of shotguns to choose from.
My favorite....