Can you elaborate on install cm1995?
Well installation wasn't the best choice of words, environment it will be used in is a better term.
Soil conditions being first and foremost.
DIP - Good for rock and rocky trench installations. Urban and certain industrial applications where there are multiple utilities and the likely hood of digging around it is high.
However DIP can deteriorate in acidic soils if the cement coating is compromised. Certain chemicals can also eat DIP up rather quickly. I saw the video of a 6" DIP lateral less than 1 year old where the bottom of the pipe was completely gone - you could see the #57 stone bedding. That lateral was for a recently built Taco Bell...take what you will out of that.
C900 PVC is lighter but more fragile than ductile however it can withstand acidic soils and chemicals better than DIP. A country water main stretching a couple of miles in sandy or clay soils is a perfect use of C900. Lighter and cheaper to purchase and install. So more bang for a local water dept's budget.
On the flip side the city I live in just replaced about 2 miles of a 30 year old 8 and 12" PVC main that was installed in rock and apparently not bedded properly. Our house was serviced by this line and it constantly leaked. It was replaced with ductile.
Just my $.02. Both have their place.