Recursive. It's more natural, functional-style, easier to debug and closer to mathematical definition. Iterative would be better for some infinite structures like streams.

There is already a trend in software automation happening now. And it is related to hardware drivers. More and more often hardware drivers are not just written by developers but generated from hardware description. If this trend catches up, then in some time we will not have any more regular developers that write software in today's languages. Instead we will have people who write specifications, people who generate code from specs and people who verify / test the resulting code against the spec. Disclaimer: I am working on such a system :).