What material best to use for press fit parts?
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.