I see many votes for the 870.
That option can quickly be decided for the buyer. Does he feel that fixed action,(ie bolt action and single action), are inherently more accurate than a change barrel gun? (obviously I do

)
Obviously, Remmington does as well. That is why they use a cantilever system on the only 870 that they pruduce that is a dedicated slug gun. They admit that 870's without it, will lose their zero.
That is the first reason why would advise against the 870.
Now lets say, I am wrong and that the 870 should be considered. Then once again I would agree that Remmington would be the most knowledgable source on which specific model to buy. They suggest... the Remington 870 SPS Super Slug 12ga, as the best dedicated deer rifle.
Problem is it cost's over 400$ new. (cheapest I can find it is 435$ new).
That would leave our friend here with next to no money for a scope. Certainly not a "quality" scope as he stated he was looking for.
I just don't see that this as a great choice given the available options.
Disclaimer: this is not meant to offend any 870 owners...after all it is "best-selling shotgun of any type in history, with over six million made"