It's likely that the bob is so popular because of its simplicity. Generally, it's an easy hairstyle to style and manage. It flatters nearly every face shape and age.
But what are the most popular bob styles right now? Let's look at a few.
Classic
The classic bob is still popular. Of all the popular bob styles right now, this is the only one that features bangs. The bangs can be very short or right at the eyebrow. The hair is usually right at the chin.
This style is popular because it's easy to style, especially for women with naturally straight hair.
The long bang
This style of bob can be very short (right at the ear) or longer, under the chin. The style can give the appearance that the woman has no bang, but the bangs are there, just very long. They are usually swept to the side. There might be some light layering, or there might not be any layering at all, though the hair is usually straight (as with the classic).
Further Reading:
http://ezinearticles.com/?Popular-Bob-Hairstyles-You-Can-Use&id=1504458