Limbo seems better for most cases. It's practically an automatic win if the opponent does not have the Rinnegan or Six Paths Sage Mode, which if they do, Kamui seems like the better option. If they were to face each other, Limbo would probably win because the Kamui user has to solidify to attack, and that leaves an opening for the undetectable shadow. If the original or shadow were to be sent to the other dimension by Kamui, then intangibility becomes useless because there'd be a shadow and an original in either dimension to attack.