RIP Justification

I think BGP is better for that job, ultimately because it was
specifically designed for that job, but also because it's now
in commodity routers for commodity prices e.g. Cisco 800 series.

+1 - for me, if I need a dynamic routing protocol between trust / administrative domains, it's BGP unless there's a good reason not to. I find it more straightforward to work with (albeit slightly more up-front to configure it and get it right) than anything else - the information available is a very clear "who am I talking to?" / "what routes do I send them?" / "what routes do they send me?". Plus I can work through the route-selection process by hand from the information displayed, and have it make sense.