Yeah, I say it's whatever feels right and what you're used to. I don't use baitcasters very much, so I don't know if this is an issue or not -- what happens when your bait hits the water and you get hit while you're changing hands? It's happened to me several times with spinning reels. Of course with a spinner you're reaching across the reel with your left hand to close the bail. Don't see much difference there.
edit: And I once lost a tarpon because he hit with the bail open.
edit: And I once lost a tarpon because he hit with the bail open.