I think Jimmy Carter's mistakes (he made a few) do little to nothing to stain his memory.
He was involved helping people, building housing almost all the way until the end of his life.
Also, found out recently btw, he put solar panels on the white house in his administration and was attempting to move the country in that direction. Reagan had them removed because it's Reagan after all, but the forward thinking is something to still applaud.
He wasn't a great president, because at heart he wasn't a political animal. If you put a Buddhist monk in a den of cannibals, the monk will be devoured. However, Carter was an exemplary world citizen. He didn't see himself as merely American, but as human. His vision was too broad for Washington, which seems to winnow the humanity out of those who stay too long.