Most likely, ranked ballots would benefit the middle party. That's not going to be universal of course.
A preferential (ranked) ballot returns a majority for the candidate that electors choose best to represent them. To win a riding, and partucularly an overall government, parties will have to be more moderate, and certainly steer away from the extremist fringe that Harper cornered his Conservatives into.
In this election, the Conservatives demonstrated that their relatively radical and marginalizing positions removed a potential for electoral growth. They were sick with their limited base. The government was to go to either the NDP or Liberals, or a coalition of the two. Only those parties had such room to grow and have ejectors make the decision to dominate the Conservative base.
From yesterday's results, a preferential ballot probably still would have returned a Liberal majority, with the NDP having won a few more seats, constrasting to the Conservatives even losing some of their closer races in Alberta.
The majority of voters will have a stronger say. Majority or plurality governments will still happen. Nothing wrong with a coalition of when they do occur. It's the right of the electors to choose representation and parties. We can dismiss cbrunnies fear mongering of coalitions and desire to limit democracy to only two parties as foolish fix of the first-past-the-post failings. We have a plurality of parties so it is in our interest to reform elections to beat represent reality.
A preferential ballot enables the possible riding-per-riding growth/representation of less dominating parties, as electors will no longer feel as though they are 'throwing away a vote,' as the electors have a second, third and so on as options for ranking competing candidates who are also viable for representation.
A far superior method for democratic representation. The least popular first choice candidates get removed from the count, and a recount resumes until a winner has the majority support. In essence, the return of run-off elections within a single vote.
A preferential ballot has has been presented by Trudeau as the Liberal preferred method of election reform rather than proportional representation.