which will really last longer?
One factor would be how much time/often are you willing to spend maintaining it.
The white wood grade is generaly what ever is cheep,it can include hemlock,pine,low grade fir things like that. Usually it is used for fencing pannels.
Cedar,western red,incense cedar is soft and open to decay but not as fast as the white wood grade. J.
Have you thought about composite type decking materials?
I have a cedar deck and a timbertech dech in my album.
Take a look for some ideas.
Here is a link that might be useful: My Album