when I machine quilt, I tend to look at the fabric and the overall pattern. If its a floral fabric but has nice solid fabric spaces, I tend to go with a floral quilting design.
Also if the quilt is for a man or woman, that has significance.... swirls etc go well on plaid fabrics.
If the quilt has a theme, that sways me toward the theme with a design. All in all, its what the quilt owner likes but I usually try to have a few suggestions