if you want to do machine quilting then look for those that have long space under the arm. Of course, it depends on what you want to spend. To me the most important feature is the space. All the machine will do machine quilting and there are many simply ones that work well. I just bought the new Janome Horizon because of the 11" arm space.
I have other machines but this was the feature I needed. I have very little interest in the 250 decorative stitches.
Space is what I want.