Using the economic indicators they did there is no doubt: St Laurent and Mulroney tied for top spot; Trudeau and Chrétien at the bottom because they made a good (at least a 'not too bad')[/i] situation worse.[/i]
When you add more abstract indicators, policy initiatives, etc, then the gap widens between St Laurent and Mulroney, on top, and Trudeau and Chrétien, on the bottom. The latter two did real, measurable political-strategic harm to Canada. In my view, and largely because of the 1969 foreign policy White Paper, Trudeau sinks to the bottom as the worst prime minister in Canadian history – including Kim Campbell and Mackenzie Bowell.
On policy achievements (UN, NATO, St Lawrence Seaway – opening the Mid-West, Colombo Plan, etc) St Laurent rises well above Mulroney – the latter was, by comparison, timid.
On balance – St Laurent ranks waaaay up there with Sir John A. and Laurier – he was, in many respects, the maker of modern Canada; the remainder have just tinkered with his model. Mulroney is just a step below that top tier. Trudeau is in a pit all of his own. Chrétien was a superb political operator but a lousy policy maker – being quite disinterested in the fate of the country.