If your jacket bunches up, it doesn't fit. Don't blame vents.
I think double vents look better when you walk but no-vents look better when you are standing still.
The ventless jacket looks fantastic from the front, until you sit on it and it becomes wrinkled. Plus, if you have any backside, it doesn't lay well. I have a few and love them, but find side vents work better for me. But I'd never argue with Cary Grant's sartorial choices.