I would choose for the multiple company option. Because you want to measure profitability between them and they are acting as separate companies. Then in the future it would still be possible for one (or more) of the companies to have two separate locations of production (sites) within their company.
You could setup intercompany between the companies so purch and sales can go automatically. And of course consolidation so reporting can be done over the entire company. Also security can be setup per company or for Accounting, Purchasing, Credit, HR, and other administrative functions over all companies.