During a downtown walk-through, a woman picked a quiet moment to ask me a side question.
"What do you think about diagonal parking?" she asked.
I allowed that I had no opinion on it.
"Oh. I thought in your travels you might have found... from other towns..." she said.
That's when I stopped the entire group to share the question and my answer.
I really don't care what kind of parking you choose to have in your downtown: diagonal, parallel, back-in or none at all. I don't care because my opinion isn't what matters, even if I've gathered up experience from a lot of other towns. Just because it worked in one town doesn't mean it's right for yours. Every town has different traffic patterns, some have highways running through them, some have college student traffic. We're all similar, yes, but we're also all different.
Yes, traffic engineers have opinions on this. But those are based on guidelines and rules and not based on testing what goes on in your town. Their opinions and paper plans make a good starting point, but not a good finishing point.
You find out what kind of parking works best in your town by experimenting. You run tests. You take some duct tape and make temporary parking lines and see what works.