My strong preference is for a variety of leaders' debates in each campaign. We have to look at the real world. The more debates that are organized by an independent commissioner, the higher the likelihood that one or more leaders will decide not to show up for some and indeed to flout whatever sanctions might be levied against them. The fewer debates that are organized, the higher the likelihood that some cheeky news outlet like Maclean's is going to reach out to the party leaders anyway and say “Let's have our own debate.”
Unless a debate commissioner is going to forbid participation in non-sanctioned debates, then I say that sort of event, let's just have a debate, let's just talk.... Say, the Liberal leader and the NDP leader have a grudge against each other and The Globe and Mail or La Presse or the University of Toronto says “Let's just have a debate between the two of you.” I think the likelihood of that happening rises to a near certainty.