Pressure Treated lumber is the most common, it is typically southern yellow pine chemically treated to resist rot and decay. Pressure Treated decks are the most affordable option . The frame, posts, joists and beams of ALL decks are built using P.T. lumber. The main downside of P.T. Lumber is that pine is not a very stable wood and has a higher tendency to split, crack, and warp and also needs to be stained every 2-3 years.
Cedar is an attractive option because of its rich color and natural beauty. The wood naturally resists rot, decay and attacking insects and it does not need to be chemically treated. Cedar is a very stable wood and much more resistant to warping and cracking than P.T. Lumber. The main downside is it does require regular maintenance needing to be stained ever 2-3 years.
Composite/PVC Is the latest material to enter the deck world. It's highly stain and scratch resistant, doesn't require finishing, and will never crack, warp, or splinter. It is also accompanied by a limited lifetime warranty and is virtually maintenance free. The downside of this innovative material is cost.