Try them out, see what feels good to you. Have an idea of your budget before you walk in the door. Don't be afraid, look at it like drawing on the fabric while driving the head ontop of the quilt, instead of shoving it under the needle. Do you prefer sit down or stand up quilting? Do you have medical issues where hand cranking would be an issue, or do you need the hydraulics? Go and have fun and keep test driving!