MS in Ob/Gyn means a master in general surgery in the branch of obstetrics and gynaecology. Obstetrics is the branch that deals with pregnancy and childbirth. It deals with the prenatal,pregnancy and post natal in women. Gynaecology deals with the study of the female reproductive system. This includes all the reproductive organs. The post graduate program for Ob/ Gyn provides a three year degree course for specialization in these two fields through a single program. To be eligible for this course ,you must have a degree in MBBS. There is huge demand for specialist in obstetrics and gynaecology in many rural communities across India . According to the National rural health mission ,rural communities  only have 23 percentage of the obstetrician that they require.
In the case of MS in general surgery , it is the specialization in the branch of treating injuries or diseases by operative procedure.  It is a three year duration course and the eligibility is an MBBS. degree.  Depending on the type of hospital that the surgeon works in ,he will handle all kinds of surgical procedures.

The pay of a general surgeon varies from ₹30,000 to more than 2 lakhs per month basing on the sector that one is employed and also experience. With more specialization ,a surgeon can increase his salary further . For ob/Gyn specialists ,salary ranges from ₹25000 to lakhs  differing due to sectors of employment.  In surgery ,to Ivan specialise  in different types such as  trauma surgery,laparoscopic surgery , surgical oncology ,pediatrics surgery , cardiothoracic  surgery and many more. With such specialization , the pay range of a surgeon can increase much more when compared to the obstetrics and gynaecology surgeon. And also with more experience ,a surgeon's pay increases much more when compared to other doctors and the demand for experienced surgeons is more.

So coming back to your question of whether it is better to start your career with post graduation in general surgery or obstetrics and gynaecology, I would have to say that it's a personal choice or personal preference because with both branches ,there is huge opportunity for employment and the pay is also good. When it come to the salary,surgeons may have a slight edge over obstetrics and gynaecology if they have more specialization and experience and are in demand .

Lastly , i would say that the decision to go for any of the branch lies on your personal preference and if you have preference for any of the branch more than the other for any personal reason,then i would suggest that you go for that specialization as the pay and opportunities for both are almost equal and similar and both would be an equally good choice to start your career as a specialist.