Definitely cleated pedals. SPD-M and other recessed cleat standards are practical; SPD-SL and Look Keo a bit awkward off the bike; but cleated pedals with cycling shows in general far more comfortable and in my view safe than the alternatives. The type of pedal you can ride with a regular show but that goes over your foot strikes me as dangerous as they won't release as readily in a crash as, say, SPD-M does (and I speak from experience with the SPD-M releasing properly in a crash). Even the traditional flat if your foot slips at any point and shoots forward (into the front spokes, as also happened to me a long time ago, triggering an over-the-handlebars crash).

But there's something to be said for those flats on an errand bike or a shorter commute. Just show up and go. No debate over finding a pair of shoes that's useful both on and off the bike. Someone correct me if I'm wrong about the foot straps/toe cages though.