Shouldn't this include Grover Cleveland (I)?
Bush 41 deserves credit for sticking the landing on the collapse of the USSR. A competent President, though I disagreed with him on many points.
Carter's image as a weak, ineffective loser is being gradually, partially rehabilitated. He got some good stuff done (the Panama Canal treaty, SALT II, the first wave of deregulation, no foreign wars, fiscally responsible, strong on civil liberties), and many (though by no means all!) of his problems were due to events beyond his control. I suspect that in another generation he'll end up just below the middle of the pack.
But the OP asked about *policy*, and, really, there's no choice -- it's John Quincy Adams.
In terms of policy, Adams was, hands down, the best President between Washington and Lincoln, and should be on anyone's list of the top three. He was a farsighted nationalist who wanted a country-wide network of paved roads -- basically the 1830 version of the Interstate Highway System -- and canals. He tried to give America a national university, an functional banking system, a real national currency, and the New World's first effective industrial policy. He was the last President to sincerely push for decent treatment and fair dealings with the Indians -- and he might have made it stick, if he hadn't been replaced by a fanatic Indian-hater after just four years. He was the first President to openly opposed the rising Slave Power. His tariff system pissed off the South, but helped catalyze the first great wave of American industrialization. In terms of foreign policy, he was a great diplomat who presided over a period of peace and good relations with pretty much everyone.
A lot of his policies didn't get passed because of fanatic opposition from Jackson and the Democrats; basically, they were determined to make him fail so that Jackson could take over. But in terms both of what he did and what he sincerely tried to do, he's the best one-term President to lose re-election /ever/.
Doug M.