Some people believe that the Liberals will benefit the most from ranked ballot voting. This is based on the premise that the middle party will get the most alternative votes: NDP voters will rank the Liberals #2; Conservatives voters will rank Liberals #2.
Also ranked voting cuts both ways on the center-left. It makes little difference to a centrist who they rank #1 or #2. So if the Liberals take a right-of-center position on economic issues, centrists can vote — #1 NDP, #2 Liberal — without worry of vote splitting letting the Conservatives win.
PV will make it easier for the NDP and Greens to get votes. It will make it impossible for the radical conservatives to get absolute corrupt power a super-majority is opposed to. It will make the Liberals work hard for their votes and compromise with other parties when they form governments.