Laura, I found that using my Davis NVF for quilting with flannel was very nice since the walking foot carries all the layers of fabric evenly through. I too found that the Davis was a bit louder than my other machines, but the treadle is one of my smoothest.
Most of the time, I use my Two Spools for piecing since it has that nice 1/4 inch foot, Singer 15-90 FMQ, Davis for straight stitch quilting and attaching binding. The Necchi Supernova is mainly used for decorative stitching and zigzag. My Singer 201 is used for paper piecing, top stitching, and button holes. Standard Rotary is right now setup for chain stitching, but it too make a very lovely stitch for top stitching. Each machine is unique, and all are enjoyable to use.
It is rather convenient to have all the machines setup to do different jobs. I just have to remember to have the proper color thread on each machine. I also need to purchase a couple more spool holders.