8/4 is stout and obviously will hold up well. You do have to be careful that the particular design you use will work proportionally with that. 5/4 or 6/4 will give you a little more strength with a little lighter look if the design works better that way. I used 4/4 for my Adirondacks (NYW design) and they have held up for 8 years now. It's just now getting to the point that I'm considering replacing them. (They live outdoors 365...)