It's not a bad stitch, but not the best stitch. I always go back to the roots of machine sewing. If there is a problem on the bottom, then it's the top thread tension that needs to be adjusted. If the problem is on the top, then the bottom is off....most often due to poor winding of the thread. I am one of the ones that do not adjust my bobbin tension. I just am not that good. Try adding a bit more tension to the top until you get the stitch you want. If that's not possible, then use the same color top and bottom and it won't be nearly as visible.