NN, I did extensive research several years ago on composite decking when it became time to replace our decking. I decided against it for a couple of reasons. One was the duty on it was quite high because it wasn't considered lumber and I went to visit a couple of installations during the summer up here in Michigan and it was extremely hot underfoot as well as on a hot August day, it was a little "springy". Has the product improved since?...I don't know but if you do have it installed, make sure that the supports (which have to be traditional lumber) are no further than 16" on center.
Nan - Yes go composite - Trex is the best value. Treated lumber for all structural members (joists, beams and posts) trex componets for rail and decking (floor). Space pressure treated floor joists 12" on centers to avoid flex. This spacing will allow you to install the 5/4" X 6" decking on a diaganol or herringbone pattern if you prefer that look. Treated wood contains toxic chemicals, although they have recently stooped making it with arsenic (rat poison). You should always wash your hands after contact with it and wear a dust mask when cutting it.
Jeri...to answer your question, yes composite materials have improved a lot. They certainly come in more colors and look more like real wood. In the summer of 2000 I built our deck at home using a product called PolyLumber. It is 100% plastic (I forget what % is recycled), and looks like tongue-groove cedar planks. It was more expensive than wood, and I had to have my bracing at 12" centers, but I don't have any problems with splinters, I don't have to stain it, and it has a 25 year warranty.
Two downsides--it can get a little hot on bare feet in the summer and it can be slippery when wet.
Thanks Doug and Aquaclear for more information. I will consider it again when the decks need to be completely replaced. Still a bit concerned about the slippery surface when wet but not having warped or splintered wood may offset that concern, not to mention the maintenance issue!