I was thinking of doing a masters in criminal psychology, but I've read that a degree in forensics science is better, which one is better?
100% Forensic Science. Criminal psychology (or forensic psychology as it's more commonly known in the UK) is solely about the roots of crime, risk assessment, the legal perspective, interventions, working with victims or offenders etc. Any MSc in crime scene management, investigation, forensic science or analytical science would serve you better to become a CSI.