Deck railings -- treated or White Oak?

[jteneyck]

All the old county bridges that are long gone now due to heavier traffic, used 3" white oak for planking.
Rain, snow, rocks, dirt......abused for 50-75? years

Like I said, I'm not arguing the durability of white oak; only that vertical applications are much easier.  In the OP's case where he wants 20 years both PT and white oak would be plenty good.  

John