I also like the idea of one main site and then sub-domains for regions. This would allow the main site to focus on the overall brand and the sub-domains can concentrate in local search and adjust content to answer the specific problems of the region. Many technologies can do this but Wordpress multisite would be good. The main blog being the main brand and then all other blogs can be put on sub-domains based on the franchise regions. You also can control the brand with the Wordpress theme on offer. You could then even extend this model as a communication mechanism as you have all the franchises in one place.
