Reasons I use nova...gestures, slide up for settings, down for notification window, double tap to turn screen off, these are customizable to user. Change icon packs. Change folder ave app drawer background colors. Resize widgets. Change color of label's, resize label's. Continuous screen scroll/dock scroll, can have more then one set of dock. Can lock home screen so you can't accident move apps around in shirt pocket. Can set up remember position in app drawer. Can change animation for scrolling home pages, app drawer. Can change speed of scrolling them.
Nova is just too customizable not to use it. And the best part, no matter what phone I get, put nova on it and I know the launcher.