If you are looking for THE best wood product, it is TWP. Log home owners who have a lot more wood to preserve than just a deck will verify this is the best. Lasts between 5-8 years. Depending on your application you would use TWP 200 or 300, definitely not the less-expensive 100.
Harder to come by, not sold in stores so you have to order it through a distributor. Here's a link:
"Scandinavian