None are any good in my opinion. Trex being the worst from my experience. Stay with real wood and re-stain every few years as needed. Treated wood will be the least expensive and tend to shrink, warp and splinter due to the treating process and being crap wood but will last ten years or so and is inexpensive to replace. Replace bad pieces as needed. Cedar is a good stable naturally decay free wood. It will last and stay looking good for a long time. Stain if you like or let weather to silver gray. Redwood, Mahogany and Teak are a bit pricey but also very stable rot resistant and beautiful. They will last decades. Stay away from that waterproofing crap. A hint to preventing rot is to wash with salt water. Fresh water will promote rot.
Teak deck, internet photo not mine.
