Robert Zubrin has discussed the "moon first" strategy, and has made the interesting observation that many of the pro arguments come from entrenched space industries looking to make a buck on existing hardware. The argument being "we already build parts to go to the moon, so let's just do that."

Personally I would love to see both outcomes. But given a limited budget, going to Mars has the advantage of providing a (admittedly risky and uncertain) possibility of extending the survival of the human race, where as going back to the moon seems to provide more indirect benefits.