In recent years, Tony Blair or Thatcher.
Brown's credit in the 2008 crisis is often disregarded, probably because people didn't realise just how bad it could've been and the conservative austerity didn't help his legacy. Had he been given another term, we'd be in a better position today even with brexit.
Although I think Attlee was the best we've seen, apart from fuelling the desire for hard socialism, he did an amazing job. Could've been better but still great.