Going by what they accomplished in office and their overall legacy. I'll give you my Top 5 with a quick reason for each:
#1 --Abraham Lincoln: Emancipated the slaves and eventually changed his views on race as a whole
C'mon, you know what he did!
#2 -- Theodore Roosevelt: The quintessential Alpha-Male
Split from the Repubs and formed the Bull-Moose party; fought for the working class
#3 -- Dwight Eisenhower: A steady, moderate leader who focused on getting things accomplished through compromise and working together
Kept the republican party from becoming ultra conservative; created the Interstate Highway system; started implementing civil rights (brown v Board of Education, sent in troops to intergrate school in Arkansas)
#4 -- George Washington: By all accounts he was the one person that the power of the presidency didn't go to his head
Kept the country together during its earliest days
#5 -- Andrew Jackson: Another strong-willed leader
Paid off the entire national debt; Abolished the National bank