Agreed with Richard above, it's hard to know what to do with "the representational content of our mental states". How would I know if the representational content of one of my mental states had changed? What would I expect to observe differently?

That said, I voted "internalism", roughly on the grounds that while I can posit things that might deserve the label "an aspect of the representational content of a mental state that depends on properties of my external environment," I don't actually seem to care about any of them.