Both are great machines! If you are quilting larger projects, the Simply will be far easier to use. The Simply also has a built in stitch regulator and can be low enough for you to sit and stitch.
The Sweet has an add on stitch regulator but it has to be positioned under the fabric that is moving so it can read the movement and adjust the stitching accordingly. The Simply table can easily be taken down if you need to store it for extra room.