What material best to use for press fit parts? I am designing some parts that should modular fit together. I am currently exploring a Lego-like design with octagonal holes and cylindrical pins.
I notice that (depending on the amount of clearance) that the fit is initially tight (to the extent that the pieces are very difficult to remove from each other), but that after a few dozen times connecting and disconnecting the parts the fit becomes very loose. I am currently using PLA. With what material would this occur less quickly/is more resistant to this kind of wear?
The sizes of the pins/holes are slightly bigger than Lego (probably similar to Duplo). Don't think that snap-fit would work in that size. Below of a picture of one of the test pieces (this one later printed in PETG).

I have an open printer so I prefer materials that don't require me to build an enclosure first. It is a Prusa i3 MK3S: Direct drive; 1.75 mm filament; max temp 300 °C; heat bed max temp 120 °C.
A flexible material, such as PETG or ABS, is probably the best.  PLA is brittle, especially after absorbing moisture, and probably would crack under continued use.
Nylon is good, but not easy to use.  With PETG in an enclosure, I end up running fans to avoid heat creep; so PETG may actually do better without an enclosure.
If you're printing to flex your print, keep in mind the the x and y axes are stronger than the z-axis, which depends on how well the layers stick together.   PETG tends to stick to the print surface too well; so I use an Elmer's glue stick for it to pull up the glue layer instead of damaging my print surface.