About the different types of wood....

Southern Yellow Pine, pressure treated (Micro)
Finished on all four sides for dimensional stability, micro pine is dense & strong, resistant to dampness and insect infestation but subject to warping. Mother Nature decides which boards will warp and there is no way to predict problems in advance.  Micro can be reasonably expected to last for many years (25 to 40 is not uncommon).

Western Red Cedar (WRC)
This attractive lumber is less likely to warp than micro. It is lighter in weight, less dense and not likely to last as long as pressure treated. It is not smooth on all 4 sides, with one wide flat side rough cut to show a texture that many users prefer. Cedar is a good choice for wide gates that are heavy and likely to sag.