Bobbins
Try to get a machine with a drop in bobbin, instead of the one that you have to insert the bobbin under the machine. Also, check out the "throat" of the machine. That is the space to the left of the needle. You want to get as big a throat as possible. My Brother has an 11.5 inch throat, which is too small sometimes to quilt large quilts. I yearn for 15 or more inches. Brother generally makes a wonderful machine. A lot of people love their Brother 1500.