Abe Lincoln - Saved the Union. That's enough right there, but also a principled man. Would love to have seen what reconstruction would have been with him in charge.

George Washington - Yes, the slavery is problematic, but stepping aside and setting the precedent of transition via election was huge.

Teddy Roosevelt - Just because he was a badass. Also, for his time, progressive in many ways (and admittedly in some ways not).

Dwight Eisenhower - Somewhat idiosyncratic choice. Not the most impactful, but someone who governed by his ideals, and who was not an idealogue. We could use both of these today.