Dear,

Each subject has its own scope. Considering GATE Exam, it is quite competitive and tough. So, I would suggest you to choose your area kf interest. You can choose any subject of your interest. Then it will be easy for you to crack GATE exam as well.

If you wish to pursue Msc. in any subject ignoring GATE, then you can go for the subject you want to do Ph.d in. As Ph.d involves research work and thesis submission, that time you need to have great interest for this to pursue Ph.d well.

Hope this sorted your query.

Good Luck :)