A policy-based IPsec tunnel with static routing is the simplest secure design for connecting two hosts in two companies when no additional future connectivity is planned. The requirement is narrow: one host in Company A must communicate with one host in Company B over a single encrypted Internet connection.
Policy-based IPsec is straightforward for this type of point-to-point encryption because crypto ACLs define exactly which interesting traffic should be protected. Static routing is sufficient because there is no complex topology, no dynamic path selection requirement, and no anticipated expansion. A DMVPN design would add unnecessary NHRP, multipoint GRE, and dynamic routing complexity. A routed IPsec tunnel with OSPF is useful when many networks or dynamic route changes are expected, but it is more complex than needed.
MPLS VPN with BGP would require provider service and does not meet the simple encrypted Internet connection requirement. Reference topics: site-to-site IPsec, policy-based VPN, static routing, point-to-point secure connectivity, WAN simplicity.