I ride with bibs and find they feel more secure, knowing they'll never creep down under my floppy skin zone...
Others here claim they chaff nipples, but not me, I had mine bitten off by an overenthusiastic gay priest... but seriously, no, they've never bothered me...
Others also state if you take the 'Natural Break' from the top side as opposed to the bottom side, it is impossible with bibs...
My 2 cents worth, I love bibs, and will never ever get shorts...