Do something that interests you and feel passionate about.
Research can be either a fascinating road of discovery or an utmost boring and frustrating task...depending on whether or not you find the subject matter interesting or not.
Hi
Yes it becomes hell if you choose a topic which is not of your intrest I would suggest go for High Power Applcations and their Designes I would suggest you to go for the Power Supply Design of LINACS which are being used for Medical Applications I find it very intresting as Currently I am working on RF/Microwave Loops of LINAc Systems check if it is comfortable for you. I think it is good thing to study you can even go for Phd