You have to take into consideration your skill level at certain techniques and the capability of your machine. I do all my quilting on an older sewing machine so I have to do something that will allow me to get the quilt through the machine. If the quilt is large then I want to minimize the number of times that I have to stuff it through the harp area of the machine so will keep designs that require turning to a minimum and stick more with straight line patterns. I also do FMQ but have to limit the time and complexity as the motor on my machine will only take so much continuous running like you do in FMQ. I like angles on quilts so will look at the pattern and see how that might translate into angles with quilting keeping the need to mark the design to a minimum and using points on the quilt pattern as reference points for my pattern.