Postgraduate certification/diploma in software engineering
Short term wise, the postgraduate certificate will help you to find a better job with a higher salary because the certificate shows that you have some skill printed on the certificate. However, whatever the technology you learn while getting the certificate could become obsolete in a few years.

Long term wise, the master degree proves that you know more fundamentals than just a bachelor. It may not help you that much when looking for a job with better salary. Some employers would think you don't have the skills they want immediately. However, you'll learn those needed skills faster and better because you know more fundamentals.

If you want to find a job as of now, you want to have certificates. If you want to be an excellent software engineer in the future, you should get a master degree