My friend and I are actually working on both right now. You'll have an easier time finding all the files for the Mark VI armor, but the pieces for the ODST armor are much simpler to construct. There are more pieces to the ODST costume, but they have far fewer nooks and crannies that might give you headaches in the construction process.
So if you're at the point where you consider both to be equally cool, and you'll be satisfied with either as an end product but want the easiest job, I would suggest going the route of the ODST armor - and not the WETA stuff. Not to knock the outrageous time and effort put into its conception, but the WETA armor has design and sizing flaws that ultimately caused my friend and I to scrap that project 7 pieces in.
The 2 biggest things to keep in mind either way, is patience and attention to detail. Without these two things, your armor will look like garbage. Too many people have either not taken the time to get the armor properly sized, haven't cared enough about accuracy of design, or generally aren't willing to put the extreme amount of time this sort of project requires to be done right. Making pepakura armor takes a LONG time. If you're not willing to take a LONG time and be careful, chances are your armor won't look very good. Don't rush it, take your time, and take care in what you're doing. It all pays off in the end.