Last 50 years would include Eisenhower, Kennedy, Johnson, Nixon, Ford, Carter, Reagan, Bush, Clinton, Bush, Obama IIRC.
Considering I don't remember much anything from the Clinton years I guess I would have to choose between Bush and Obama. And since Obama isn't even through yet and could go either way with it. Bush I guess.
I'm not saying Bush because 'zomg he's not a communist like Nobama!111!' but because honestly anyone 20 or under (my age group) really can't say shit about who was the best president since most of us only really experienced the last 2. (Preemptive shut the fuck up Sh1fty)
From what I have read about the other Presidents in the last 50 years I didn't experience- Ford, Carter, and Bush senior didn't have remarkable presidencies or were anything to write home about personally. Going by what I have read though, I think Nixon gets a shitty deal historically because of that whole Watergate thing. Opening up relations with China, ending the Vietnam war, and a few other great things seem to get buried under the Watergate scandal. The Eisenhower years also seems liked a pretty good time and his tenure was pretty stable aside from that whole Little Rock thing. Going back a few more years and I would have said, without a doubt, Truman. Again just going by the things I have read.