I'd second pep being the strongest/most durable but it also depends on how you treat the stuff.
I can yeet a foam helmet across a room and know it'll be fine. Pepakura if treated well will outlive you. 3D prints if made from the right material can be extremely strong but it's often a stepping stone to moulding and casting objects which is generally a more durable/easily replaceable alternative.
Prices of tools are generally the deciding factor. Good quality tools for a pep build are dead cheap and you can pull off a SPARTAN-III for around $500 if you try but the time investment is huge. Foam is in the same ballpark as a pep build for setup costs but the time investment is a bit lower per suit, just expect to build one or two before getting to a point where you're happy with the end product. 3D printing a full suit can be done for about $500 but the number of pieces and huge number of assembly and sanding hours is daunting, get into the $1000-$1500 range and a suit will be considerably quicker to produce (400-500 man hours and ~2months of machine up time). Moulding and casting, take out a small loan or sell your car to build one suit, then make dozens more that are identical to recover costs.