The first one is OK.
The second one isn't your best. I don't like it too much because your focal point is at the right, which it shouldn't be. It should be either in the middle, or if you do decide to put it in the right or left, make sure your signature flows to the opposite side of the render.
The third one has too much of one same color. If I can guess, what you did was picked a hot pink color - use Clouds - and used one brush with a certain setting. You don't want to hurt the viewers eyes, because that color hurts mine.
I don't work too much with abstracts, but I can say that you should download different kinds of brushes, and test each of them out.