The course that is best for you will largely depend on your current role or the role that you are aiming to fulfil:
If you are a construction site manager, project/contract manager or are aiming to obtain such a position then the SMSTS (Site Managers Safety Training Scheme) course is almost certainly the course that you should be undertaking. Generally the SMSTS course is seen as a progression from the SSSTS.
For construction site supervisors, team leaders, foreman, etc then the SSSTS (Site Supervisors Safety Training Scheme) course is invariably the course you require unless you are looking to step up into a construction site management position.