If you haven't yet tried them out, I'd suggest going to a quilt show and trying them all out. All three of those: Martelli, APQS(makes Millie), and Handi Quilter, are companies that have been around for a good while and have good reputations for service, etc. It really comes down to individual preference, which is why I suggest going to some shows where you can spend time trying them all out side by side.
Rob