There are three theories that I know of...The Traditional Geography Theory, with the Book of Mormon encompassing all of the Americas, the Mesoamerican Limited Geography Theory, and the Great Lakes Geography Theory. What makes one more plausible than the other? I know FARMS puts a lot of effort into excavations in Mesoamerica, but I would think that the Great Lakes Theory has value, too. Most notably, there's not the problem of multiple Hill Cumorahs (I KNOW a suggestion by the Mesoamerican group is that Moroni wandered up to Western New York in his decades of wandering after the events of the Book of Mormon took place). And there seems several scriptures in the Book of Mormon back up the Book of Mormon happening in North America exclusively. Should there be more of an effort there, also?This is not really an answer to your question (is there any way to answer this one?), but just an amplification: if you're going to move away from the Hemispheric model, you also have to deal with a guy named Zelph.
Anyways, where do you believe the Book of Mormon took place? If you have a good link, please send it my way :-)