This has been asked before. It's better to leave it in Drive, the engineers assumed you will have it in Drive without moving for a few minutes and designed the system to accomodate it. 

Leaving it in Drive also allows you to get yourself out of a situation more quickly if an accident occurs in the intersection, etc. 

If you're waiting for a train, you might put it in park. If it's really long, you might turn the car off. 

It is illegal to operate a motor vehicle in neutral in most places.  Check your state's motor vehicle code and leave it in drive.

Besides the safety reasons, the damage you cause to the transmission by leaving in drive in much less than if you put in park and then switch back to drive.