The main difference is the 2 day course is held at weekends, and the 3 day course is held during the week. They cover the same content, but the 3 day course has shorter days. If it is possible for you to attend the 3 day course during week, we would recommend you do this, as you will gain an extra lesson practice and more one-to-one time with your trainer and, therefore, more hours of training on your certificate.