Is there any real difference over placing Access Points over Wireless Extenders? How do you know when to use one or the other?
My personal recommendation is to never use extenders/repeaters if you can avoid it.
Repeaters do just what they say and repeat a signal they hear. This reduces the overall performance of wireless, as wireless is a shared medium which means only one device can be "talking" in the same area at the same time. Each frame (in both directions) is now transmitted twice, taking up twice the air time and halving the actual throughput you can achieve.
In addition, repeaters can introduce or make worse other problems. They are really only suited to home environments with few devices and air time to spare, not in a campus environment.
Additional access points add extra capacity by using multiple channels and creating some separation between devices on the same channel. Keep in mind that a campus wireless deployment should be planned properly before implementation. It is not something you can just "throw in" like you may have been able to get away with 5-10 years ago.