Free-motion quilting can be very taxing on your sewing machine. Sometimes the work is just too large to fit, or the sewing machine’s arm can’t quite make it through.
The Bernina Activa series has some good quilters in it, but they can be unwieldy at larger size work. Look at the Bernina Activa 145S or Bernina Activa 125. Bernina also makes the Artista 730E or 630 which have a stitch regulator for free motion use. They are complex machines, but will do the job.
The Singer 301 is also a good choice. It has lots of adjustments and a powerful action so it can sew through multiple layers at a time. It could be the
The Viking Sapphire 870Q has some good and bad. It was made for free motion quilting, but some people don’t like it for quality reasons. I’ve had mixed feelings about some of Viking’s machines, but some people swear by them. Try them out before buying.
There are a couple of other machines made just for quilting. Pfaff makes a Quilt Expression series that let you ratchet down the arm speed for free motion quilting.
All in all, the best sewing machine to do free-motion quilting would be a specific model built just for quilting. If you like the Bernina’s I would recommend them - many people have had great experiences with the brand, and the Activa series are very feature packed.