Which filament is best for outdoor use?

From my own experiments in Florida... PolyCarb is the best and second-best is BluPrint (Taulman) at least as far as withstanding high temperatures. Just my 2 cents... Everything else I experimented with pretty quickly warped or otherwise deformed. Some were still quite strong, but they did not stay "intact".

Of those two BluPrint is easier to print with something like the Robo (which struggles even with ABS given the open-bay nature). But with experimentation you can get it to print ABS or PC ...