This is going to turn into a debate very quickly, because there are about a million pep files everywhere for helmets.
For MK VI, you're either looking at Slyfo's model (In the previous post), at flying_squirl's model,
http://405th.com/forums/index.php?showtopic=5089
The last one I could find would be dannifood4less's helmet. It uses flat pieces, so there is not a lot of folding, and it comes out pretty smooth.
http://405th.com/forums/index.php?showtopic=3719
(These are the only helmets I could find, there are a lot more detailed versions, I just found these very quickly)
If you haven't had any practice with pepakura, you might want to start off with the low detail file and move up from there.