I have studied Traditional Catholicism (e.g., SSPX; various forms of Sedevacantism) so perhaps I am the only LDS apologist who has an interest in this debate, but the following was a very good debate (I was pleasantly surprised by how well-behaved Peter Dimond was):
Sedevacantism Debate: Are John XXIII Through Francis True Popes? Jeff Cassman Vs Br. Peter Dimond