There are plenty of 'better' ones...but it depends on the situation that you are using them in.
The Omnibounce is great when you are bouncing off the ceiling or a wall. It allows some light to bounce and some to go directly to the subject. A simple bounce card can do the same thing. There are also other accessories that do the same thing, to one degree on another.
If you are shooting directly at your subject, or if you have no surface to bounce off of. The Omnibounce is useless. The only way to make light softer, is to enlarge the source or move it closer to the subject. The omnibounce is only a tiny bit larger than the flash head, so it doesn't really make the light softer....but it does spread the light around...and it's wasted if there isn't anything to bounce off of.
Many other accessories fall into this category...the Fong Lightsphere for example. It's great in smaller rooms but very wasteful in large rooms or outside.
If you can bounce the flash off a wall or ceiling, that is best...and most accessories will help in this situation by splitting the light.
If you are shooting the flash directly at your subjects, then may want to enlarge the source as much as possible. To do this, you could use a flash mounted softbox or use something like THIS.
big softboxes and umbrellas are good if your flash is offcamera - but are way too big if its mounted on camera (or on a flash backet).
I prefer the Lumiquest softbox (its a softbox, but its small enough to be mounted on camera and won't even block AF assitance lights if your flash has them),. I find it works well inside and outside - even for macro work
If your looking at studio work with lights on stands and such then umbrellas and proper softboxes are the way to look - and I know nothing about that area