I have used both the face tools and from my experience, I would recommend Gua Sha if you looking to define your Jaw line. Jade roller is good but its mostly for better penetration of serum and oil on your face. Gua Sha is helpful to drain lymph fluid from the face which sometimes makes the face looks fluffy. Gua Sha is used to give a facial massage but you would have to be consistent and patient with this tool. I started noticing the result after 3-4 weeks of using it twice daily in the morning and at night. A lot of celebrity like Gwyneth Platrow, Kendall Jenner and Miranda Kerr and many more swear by this.
Refer to this picture and start using Gua Sha in same directions.