A stitch length of at least 4 mm is important for basting. A stitch width of at least 4 mm is important for zigzag, satin and decorative stitching. Testing the buttonhole procedure is very important, because a bad buttonhole can destroy a finished garment. Most machines have this mechanism in various forms. Some require manual turning, some are 4 or 5 step processes and some machines feature a 1-step process.
Decorative stitches are another consideration.
The number of stitches is directly related to price. Other available stitches will increase the price so review your needs and choose a machine that reflects the sewing you will do. Bobbin winding may also take place on a separate spindle or when the bobbin is in the sewing position. Check to see if the winding stops when the bobbin is full. Dropable feed dogs are a must for free motion work, such as darning.