sprties give realtime rotation, scaling, alpha function and sprite automatically track positions, sprite x or sprite y, you can set draw priority with sprites easily, as well as use box collision easy. sprites have alot of built in handles that you may or may not need but using image you will have to make handle function yourself. neither is noticable faster or slower, sprite may take some getting used to but they can really shorten you programming time. That said I still almost always use paste image for my backgrounds, no real reason just habit I guess.