(OOC: Not sure if this needs to be in Before 1900, instead, but I think its possible with a PoD after 1900. To clarify the abbreviation, its the United Kingdom of Great Britain, Northern Ireland, and Canada.)
IC: Its been nearly a century since the Act of Union that brought Canada into the United Kingdom, and there have been many Prime Ministers in that time - some quite good, many mediocre, and a few embarrassingly horrid.
Who, in your opinion was the best, and who the worst, and in each case, why?