Hi,
There are lot of discussions/blogs regarding this topic, try searching before you post so that you can get more info than in threads.
Re usability is the main difference. In OO ALV you will be having more flexibility like placing multiple containers so that you can report multi reports like header and item and other details in single shot/single screen. Docking properties etc....
what i like in OO ALV is
In OO ALV, you don't need to worry about the application toolbar designing and adding some functions
we will have more time to concentrate on our business logic rather for designing.
everything is instance driven less PF-Status work required... etc
thanks
SaiKrishna