Well there are no
wrong files out there. It's really a matter of preference. Every odst set on here has it's own style and features, as well as how difficult it is to make. One of the most common pep files for the helmet was made by Rundown, though I am not sure if he has done a whole set.
The two members with the largest selection of files is Kirrou and Nightshade to my knowledge. Both of them have made really nice models that have worked for most of the members on here. (sorry if I missed anyone) The design of the files are different so you may want to check them all out and see what you think you can build.
I highly recommend Kirrou's new HD odst helmet, he has really streamlined the design for simplicity and accuracy. Though you may want to ask him about smoothing the pepakura file out so your build looks better
Here is a link to Kirrou's odst file base:
http://www.405th.com/showthread.php/22471-New-Hd-Odst-Game-Accurate-Pep-Files
And here is the one to Nightshade:
http://www.405th.com/showthread.php/17214-Halo-3-Odst-Pepakura-Armor
I also have a few files on my thread (link in signature) but most people find my work a bit too tedious to build. Depending on what odst you want to do may help you narrow your search. Nightshade and Kirrou's files are based more on the ODST game itself while mine are strictly the simpler odst's from Halo 3.
I haven't seen any files for Reach Odst's but I imagine that's coming, just not from me
I already have other projects lined up after this.
Hope this helps. Good luck with your build, trooper.