Within my own lifetime? Reagan, hands down. A witty, fatherly, 'happy warrior', whom I would not hesitate to have as a professor, boss, or in-law. The kind that would chide you for being a dumbass, but you'd still feel good about it. Four words still make me smile, "There you go again."
Real Presidents: T.R , Calvin Coolidge, Truman.
Fictional : the one from Independence Day. President Andrew Whitmore(?). . . All the hot of Kennedy, the 'happy warrior' of Reagan.