[Zeke]

There is and always will be debate on this. One theory says that the "smile" is up because the annular rings will tend to straighten out, or create a crown. Another says that the grain will lift more with the smile up. The prevailing weather will have a lot to do with it. In the desert, I might place the smile down as a frown. The wood will cup anyway. I tend to put the best side up regardless.

Sealing the lumber top, bottom and ends after it has seasoned a short time will have many benefits.

Vertical grain, quartersawn and composite decking are all better solutions.