What I'm going to do is give you the same advice that someone gave me about 20 years ago when I went looking for a new slug gun.
If you have friends who own a model you are considering, ask them if you can go out shooting with them, and if they would mind letting you try out what their slug gun. Think of it as a test drive using the same make and model car as the one you want to buy, without the hassle of having to deal with a pushy salesman. After you try out the different models, you will have a much better idea of what will and won't work for you.
After you have decided and purchased your slug gun, go out and but a couple of boxes each of the slugs (Rifled for smoothbore, sabot for rifled barrels) for each brand that you want to try out. Go to the range and shoot some 3 round groups. Pick the slugs that perform best for your gun, and sight in using them ( your not after a bull's eye, just a satisfactory group on paper, then you do the sighting in.) At that point, you will have a shotgun you will be happy with for a long time, and you will know you are good to go when you go afield.
I can't reccomend a certain brand of shotgun or slug to you because I'm not you, and no 2 guns are identical in their performance and ammo preference. I can however tell you what I use. I use a Mossberg 185d 20 Ga. that delivers the best performance with Remington 2 and 3\4 inc Sluggers. you will not find them new as they were made in the late 1940s, but you can buy one for under $100 if you can find one that looks a little rough, and you work on it yourself. I paid $80 for the gun, $25 for the bluing kit and the steel wool, and I spent about 4 days working on it. Mine came with the interchangeable choke tubes that screw onto the outside of the barrel, the tube wrench, and an aftermarket peep sight. I can bust 3 beer bottles set up at 50 yards with it with ease, and it will shoot minute of deer at 80 yards with no problems at all. Pretty good deal for $105.
Deals are out there, you just have to look for them. Hope this helps, and best of luck.
Is it better to do the right thing for the wrong reason, or to do the wrong thing for the right reason? If you do the wrong thing for the right reason, is it still the wrong thing?
Si vis pacem para bellum.
There are two ways of doing something. Right and again.
If you can't be good, be great at it.