From the surface of things, Reagan was able to see through an end of the Cold War without bloodshed whereas Bush has really fumbled this terrorism ball. Reagan, though he was incredibly old & slowing down in the upstairs, had experience on the national political level since 1964 (he did alot more for Goldwater's doomed campaign in one speech than everyone/thing else combined) and was thus far more qualified in terms of knowing whose advice to take, etc than Bush had coming in (and, apparently GWB is still very lacking in this area). That doesnt necessarily mean that the advice they chose to take led them to make opposing policy decisions but Reagan certainly had a legup on Bush in terms of political and policy knowledge.
The big difference is that Reagan didn't have his hand held tight by those with a neoconservative mindset re: foreign policy. Unfortunately (especially for Reagan, who is credited by real conservatives as the successor to Barry Goldwater), they share a huge similarity in terms of how much money was spent during their administrations.
On a personal note, one big difference between these two presidents - had I been of voting age at the time, I would have voted for Reagan in 1984 (I would have gone with John Anderson/Pat Lucey in '80 as Lucey was a homeboy and the election was a guranteed Reagan win anyway).