The one I am using is Creative Drawings. I have used Pallet and Master Works both from Baby Lock. Creative costs about $700 but is by far the most robust. It will create designs for any machine.
All of them have a huge learning curve. But once you get the hang of it, you don't want to stop. Right now I am working on 12 spring flowers for a quilt. These motifs were all taken from photographs. I am so excited to finally understand this software enough to feel confident that I can do almost anything I want to do.
Which ever software you choose, find a yahoo group that supports it. Just like this group supports all things quilting and you can really learn from it, the same is true of a digitizing group.
I wish you the joy I have found in digitizing and being able to combine three of my favorite things, embroidery, quilting and gardening.