This is not really a great comparison... Pepakura will just end with you casting the paper parts in polyurethane which is just as rigid and uncomfortable as printed parts only you have to invest WAYYYY more time and money into the Pep route than just 3D printing, especially if you already have a printer available.
Go the foam route and you'll look like a 10 year old made the suit in his bedroom on his $2/week allowance, foam suits are all trash (IMHO). They are too porous to look like metal, it's too flimsy to hold it's shape, it's too heat sensitive to leave in a car (also a problem if you print with PLA), it's too thick to properly render small details/parts, it makes small parts look too bulky (due to it's thickness) and it just screams "cheap amateur suit".
Now that I ruled out foam realistically your processes are going to be either:
Pepakura
- Print out pep patterns
- Cut out patterns
- Spend many many many hours gluing the patterns together
- Go buy resin and respirator to apply the resin to the part,
- Add tons of Bondo then sand, sand and more sanding.
- Now you're finally ready to make a mold of the part which means buying mold making supplies
- Once you have your mold you will need a two part polyurethane mix to slush cast the part
- More sanding to clean up the final cast
- Finally you'll need to paint it.
Pepakura Materials Needed
- Paper
- Lots of SuperGlue
- Fiberglass Resin
- Respirator
- Bondo
- Sandpaper
- Non-Sulfur Clay (for the mold)
- 2 Part Silicon Rubber (for the mold)
- 2 Part Polyurethane (for the cast)
- Paint
3D Printed
- Cut the part into printable pieces (depends on printer volume and part size)
- Print the parts
- Sand down any print flaws
- Glue pieces together (assuming you cut the part)
- Apply Bondo, then sand, sand and sand some more
- Paint
3D Printed Materials
- Filament
- Lots of SuperGlue
- Bondo
- Sandpaper
- Paint
As far as it being uncomfortable? Welcome to costuming, you're often going to have to choose between something that's realistic and accurate or something that's comfortable. Actors constantly complain about the makeup/costumes for good reasons, welcome to the club
Personally I like to bring my main cosplay which will probably suck to wear (I'm printing an Ironman suit and I fully expect it to be miserable, but it'll look awesome) but also something that's light and comfortable to change into when I just wanna relax be comfortable and enjoy the con.