Well if you're unsure, you could try Tony's one. I plan to give it a whurl one day. From what I've read, the general concensus is that if you use munich I, your entire grist should be made up of munich and vienna (and speciality grains if desired), whereas if you use munich II, you can use Pilsner as well. The presence of crystal is up for debate, although my conclusion is that it should be left out as you do not want a sweet finish or any caramel notes at all.
Based on all of my research, Tony's recipe appears very on track with the authentic style (there are a lot of inaccurate interpretations out there), so I'm going to start with his and then make any changes I feel are necessary to suit my palate. I have seen respected brewers suggest starting with 33% Pilsner, Vienna and Munich II as a base and to make changes to suit after that, but I'd rather go with Tony's to start with as he is a veteran and cares about replicating the style too.
Call me obsessed, but I love me a good Marzen and I hate the fact that their availiability commercial is usually seasonal. Every day is a good day for a Marzen!