A medium sized river about 4 miles down the street from the house has loads of smallies and you'll never see another fisherman all day.
On my best day there I caught 83, but I was talking to a fella last week who fishes 20(?) miles down stream, he told me one day last summer he and his son caught over 300

My second choice would be the same as Jed's
The main branch of the Penobscot River in Maine may be the best smallmouth river in the country