With dynamic routing protocols, neighboring routers exchange information about routes and eventually disseminate routing information throughout a whole set of routers. In the WISP context, good reasons for using these protocols are (1) to relieve the staff of having to maintain static routes in all routers, and (2) to provide automatic fail-over in case a link goes out of service. Drawbacks to dynamic routing include the initial learning curve and startup effort and the increased difficulty of troubleshooting problems.
RIP is one of the earliest dynamic protocols, having appeared in BSD's original routed. Its relatively primitive nature gives it both advantages and disadvantages. It is relatively easy to set up and understand. It performs best at a small scale, and has both limitations and pitfalls at larger scales. RIP is the most mature and probably the most widely supported protocol.
OLSR is a relatively new protocol developed for mobile clients in wireless meshes, but it can be used for basic dynamic routing purposes such as automatic fail-over. It simpler than RIP, but not widely supported among different vendors.
OSPF is a well-regarded, more complex and more sophisticated alternative to RIP. OSPF on StarOS (and elsewhere) seems to have mixed reviews in the forums.
BGP is oriented toward the largest scale, such as the entire Internet. It might be used by an ISP who has multiple attachment points to the Internet from different upstream providers.