Here is the next answer to this design test
The top design is the better one because (1) it is balanced, and (2) there is contrast of direction with the dominant (left oblique at 75 degrees) in harmony with the vertical short sides of the enclosing shape. This produces a better balance of direction by re-enforcing the verticals or short sides that otherwise would be overpowered by the horizontals or long sides. This results in a stronger and more interesting contrast of direction.
It is interesting to note that the author and designer of this test, Maitland Graves, intentionally made these images minimal and abstract. He felt that using realistic subject matter would tend to suggest associated ideas and prejudices, that the test taker could be influenced by factors foreign to pure design. (such as color preferences)
As a reductionist/minimalist artist, I find these to be very instructional. These types of abstract designs are the things I look for everyday in the real world. They are what catch my eye. Patterns in the everyday.