I started with Seven Samurai as both my first samurai film and Criterion in the DVD days and I've never looked back
. Yojimbo and Sanjuro are very safe choices too, though they don't feel as traditionally samurai as Seven Samurai. They're formatted more like westerns, which Kurosawa was inspired by (and in turn, Leone inspired by Kurosawa to make the Dollars remakes). The Hidden Fortress is my fav. Kurosawa film, but I like it more for the action/adventure feel of it, rather than anything particularly to do with samurai action. Harakiri is another fine choice that you can't go wrong with.