Use of OR is more efficient.since Descriptive programming 
or reading property values from Excel sheet and create a 
object will take more time.This you won't able observe when 
you do it for 1 or 2 object. Do it for one complete 
scenerio and you will able to figure out the time taken for 
creating objects.
So Use Descriptive programming for very very less objects 
in your complete application where it is not working with 
OR.
You can observe how much time it will take while reading 
values from excel and creating objects if you automate some 
30 testcases.
OR is best feature provided by QTP .Use descriptive where 
operations not performed some objects. you will find some 
dialog boxs or messageboxes.so there use descriptive 
programming.