First: I don't own a combo. But I'm European and have probably shot, handled and seen more of them than most Americans.
I don't know which brand is best. But I do know which two brands will be suggested here: Savage and Baikal. Those are probably the cheapest you will find, not the "best". Of the two I would take the Baikal hands down. "Best" would probably be a Krieghoff, Merkel or other European up-market gun at $5000+ (or $40,000+ if you want
really fancy wood and engravings
). There are probably dozens of brands, mostly Italian, in the +/- $1000 range. That's a very rough guess at what prices would be in the US, and most of those guns are probably not sold there in the first place.
A rimmed cartridge will give better extraction in a break-barrel gun, but .308 works if that's what you prefer. European combo guns are available in almost any caliber you can imagine, especially the expensive ones. I guess it depends on what you plan to hunt, and what calibers are commonly available in your neighbourhood.
There are S/S combos out there, but the vast majority are O/U. Some are available with shotgun/shotgun and/or rifle/rifle barrels on the same action.
The advantages? It's a compromise. To me at least, a combo gun is a shotgun first and rifle second, and I would choose the gun based on that if I were to buy one. I would hunt with it as a shotgun - birds, hare whatever - and the rifle barrel would be there if I had a shot at stationary small game outside shotgun range, or I had a tag for say deer and came across one while primarily hunting small game. Or maybe beaver, where I can imagine situations where either a shotgun or a rifle may be best suited for a given situation. All this is hypothetical as far as I'm concerned, I don't own a combo, and I've never hunted deer or beaver.
I don't know if this is helpful, I just thought I would mention that there are more choices available than the Savage that usually pops up in threads like this. (And I think that every single combo gun I have ever shot or handled is better than the Savage, but that's just my opinion.)
