Who do you think were the best and worst presidents of your lifetime? To any degree you want to elaborate, why? If you are not from the Unites States, you may specify an American president, one of your national leaders, or both. For that matter, if you are American and you are sufficiently impressed/unimpressed with some other world leader, feel free to mention that leader.
Suggested definition of "your lifetime" is any president that you directly remember (a compromise between completely second-hand impressions and informed adult impressions). In my case, that would be Lyndon Johnson, even though Eisenhower was president when I was born, and JFK was elected soon after. As long as you're willing to 'fess up, it would be useful to know the first president you remember.