I know everyone puts Kennedy up in there top 5 presidents ever, but personally, I feel while he was a great man, and good leader he was never faced with any adversity. FDR, Lincoln, and Washington are often ranked in the top 3 for their leadership during trying times. For example, FDR handled the Great Depression and WWII with skill and determination and due to his presidency, America became a superpower. Lincoln did what no president ever did, by rebuilding a separated nation. Washington handled starting the nation with grace and set precedents for future presidents.
Anyways, my list would probably be:
1. Abe Lincoln
2. FDR
3. George Washington
4. Thomas Jefferson
5. James K. Polk
By the way, if you don't know who Polk is, look him up. Everything he said he was going to do during his campaign, he actually did during his presidency. And the only reason he wasn't elected to office a second time was he hated the job and didn't run.
Also, for the record, I'd put Kennedy somewhere in the top 10.