The best decking material would be something call TREK. it's a little on the pricier side but well worth it. it's a very hard plastic substance made to look like wood. it is slip resistant and will not crack under strenuous conditions. I wouldn't use anything else.
The best material for a deck in harsh climates is composit decking. Composit decks are more expensive but will last a life time in any harsh climate. Green treated lumber would also be a solution but will require more yearly maintence. Go with composit decking. It is worth every penny spent.