Being in that business, I can tell you many great products and many products that are only bi products of great advertising budgets only.
great products: CWF-UV from the Flood company, sub of Sherwin William's, Any product from the Wolman Company for decks and fences, Culprinol from Sherwin Williams.
**** Note, all the above need to be re applied once every other year and probably more often in your region. However, UV is the worst culprit of deterioration, and your area might not have that as a main problem. Where here in Texas its a big factor.
Any product from Thompson's is not worth the trip to find it.
Remember, the above "great products" will penetrate the wood and if its a new or un treated wood, the first application will literally soak up quick. so you need to build a base and once that is obtained, each subsequent coat will do a better job.
CWF is my favorite. My rule of thumb is any preservative that can be sprayed on with a deck sprayer is not any good. A good product MUST be hand painted on, not even rolled.