870 and get the barrels you want (rifled for deer, chokes for birds, etc)
Assuming your looking at lowest cost...I'm in this camp too.....I'll add the Mossy 500. Someone mentioned the combo, which is likely your best bet.
Both have reasonably priced and readily available barrels to make your gun into pretty much anything you want. You will also find used barrels easier as well, and cheap.
I will add, that if your looking for an 870, the older ones are better.....I've seen issues with newer ones alot.
If you can find a good used 1100 or 1187 auto, you will find barrels for that too readily.
That said...for pump guns I'll take a model 37 Ithaca over anything, with the exception of maybe a Model 12, but it's not as versatile as barrels on old models need to be refit at high expense. And even if it does fit a post 855,000 model, the barrels are not cheap bought from Ithaca.
I also like the Benelli pump, it's simple and works like a charm, but again, the barrels to make it versatile will set you back some cash. My son has one and we priced a deer barrel for it....you can buy a new GUN with the barrel on it for almost the same price.