A Diploma is basically a certificate for completion of a specific course generally a professionally or vocational course. The difference between Diploma and higher studies is that Diploma is generally shorter and very specific to the profession compared to higher studies or professional studies.
Below are the pros and cons of diploma which will help you analyze if a diploma works for you or not.
Comparing Diploma to post-graduation, Diploma has lesser exposure since it relates to development of a specific skill set
A diploma does not provide a general coverage but covers all the important topics of a specific area. So only if you have a specific subject in mind, diploma is useful.
It would be best to take up a full-time Diploma if you are unable to pursue under-graduation for some reason and want to take up a job after 12th. However, if you have completed under-graduation then get a job and take up a Diploma (not full time) in the field in which you are working.
This will provide you an expertise and deeper acumen, understanding and comprehension of your work and field which will prove to be valuable for your job.