I find scrappy quilts are my least favorite because they so often read to me as very chaotic and busy. That being said, there's a few instances where I like them: 1) if they've got some sort of resting point for the eye like (solid and consistent) sashing or framing around the blocks, 2) if the overall quilt is a color gradient (either all one color from light to dark (or vice versa) or, my favorite, a rainbow color gradient), or 3) if the overall pattern the blocks are arranged in is so strong it pulls all that chaos together (I've seen log cabin blocks arranged with contrasting colors that allow these kinds of patterns to be made but the overall effect has got to be BOLD to pull it off)