A Dilemma - (part 1)
There are many products on the market today to choose from. The bigger names are Trex and a AZEK. They typically command a higher price, but they have gone through some rigorous evaluation and testing and are proven products. I recommend that you always go with branded names, especially on a deck product that you expect to last. These well-known manufacturers are offering 25 year warranties with the proper installation of the product.
There are lumber alternatives that fall into 5 general categories