No Prime Minister is perfect because they tend to come with Party dogma attached. So it is possible to find flaws in everyone of them, including Churchill and Thatcher.
The standard of Party leader on both sides has been poor for a generation. Hague, Howard, Duncan Smith, and Cameron were universally terrible. I actually think May is better than all of those, though it is too early to give a definitive verdict.
I am not exempting Labour from criticism either. Callaghan, Foot, Kinnock, Blair, Brown and Miliband were all bad. (The exception, John Smith is a case of the best Prime Minister we never had). Corbyn is a refreshing repositing of the Labour Party to its true meaning, unfortunately he couldn't run a tuck shop nevermind a national party.