Ultimately, my personal thoughts say Laura. I don't want to assume that we can casually allow Madder to Exorcise if there are any other ways to raise the Stalker's awareness of us, AKA Dark Event 2. Also, as Diplomacy costs no sanity, Laura can actually remain active until she needs to do anything other than Diplomacy, which is considerably more flexible and also doesn't involve others needing their actions to rescue Madder.