Well flaps help not only to block rain but redirect it when it's running down your jacket.

I have an arcteryx jacket with waterproof zips, when it's wet, all bets are off. The thing too is if you're in a normal rain that's fine but when the winds are blowing, if they're open, rain will find a way in. Bonus though, the hood's sized to fit a climbing helmet so it goes over my bike helmet easy.

For biking, 2 way's are the best, you can open them up till the pits, leaving the torsol portion closed, because you're hunched over slightly, the rain won't get in and it creates a nice breeze as you're riding.