Action bar becomes popular after it launched in android 3.1 version. Using action with Fragment avoid overhead of maintaining stack of activity. But customizing action bar style is pain. We should thank to Jeff Gilfelt for his great work. He provide tool of customizing action in unique style.
Just customize action bar style like editing a photo in Photo Editor and it will provide you complete resource with layout, style and draw-able (which include hdpi, ldpi and xhdpi images)
You can use Sherlock Action bar also if you have backward compatibility issue. You can customize its look and feel.
It provide you complete control on customization on android action bar style. you can change action bar Tab bottom line and all other thing related to it
Here Go for Action Bar Style Customization URL