Maybe this is a MTB-background thing, but I've never seen anyone hop up a curb with loaded saddlebags, and I know I never could. That alone kills the deal for me.

It's also a lot harder to pick up a loaded bike and carry it up stairs etc. I used to use saddlebags for long-haul trips, but I think nowadays I'll vote backpack, at least for trips of less than a hour or so.