I've had just a little bit of exposure to the new decking materials and haven't seen one yet that I like over PT Wood. In addition to there upfront price, you really need to have your joists on 12 inch centers. Even then, some will begin to sag over the years.
I screw down the decking on my projects. I like to snap a chalk line to get them all lined up too. Then I screw them down until the heads disapear into the wood. Two screws per joist for the length of the board.
If you do go with PT wood decking, buy it a month or two before you install it. The shrinkage in that first few weeks will be severe. Then it will stabalize and you can get your spacings pretty accurate.
Don't spread them out, just stack them outside so they will keep from warping while drying out. Home Depot and Lowes will take warped ones back, so don't mess around with any of them. No point in it. I ususally buy a dozen extra with the plans to return what's not used.
I like the look of weathered wood, but Thompsons has there water seals in colors now. You just spray it on every year and it looks great.
