The difference is really billing and convenience.
With a 1 person, [more than 1] device package, it's billed to one person and you can knock each other off if you log in with an additional device once you attempt to log in with a new device when all the logins in your package are currently in use.
With multiple 1 person, 1 device plan, that's good for when you want it billed to separate people.
Really as long as you don't care about individual billing, the 1 person, [more than 1] device package will always be a better deal.