I think most new machines have some common features such as feed dogs down, and needle down functions. For free motion quilting I'd be looking for features such as how much room is in the throat of the machine. How big is the sewing platform. How good is the lighting. Can the presser foot be raised or lowered by using the foot pedal. Does it have a special foot for free motion.
You might try free motion quilting on the machine you now have. Decide what you like/dislike about sewing on that machine and what features you wish it had.