All job roles will be rewarding, provided you are passionate about what you are doing. It can be anything in this world. As regards HR, there is no one particular domain area, in HR, will be rewarding. Again, it depends upon how much of commitment and passion you display in your job role. HR is all about R to R ie Recruitment to Retirement. Incidentally, my own firm, is called R2R HR Services. The importance of various domains in HR varies from industry to industry. You should decide, in what kind of industry where you want work. IT companies will not have manufacturing base, so you wont learn anything about Industrial Relations. In IT companies, recruitment is outsourced, so you wont learn anything about recruitment. If you work in an Indian IT company, there will be requirement about pay fixation for overseas employees. Therefore, HR skill varies from industry to industry. If you are successful, then your job will be rewarding. It is up to you to decide in which area you want to excel. So, google and read everything about various HR roles in organisations and then come to a conclusion.
Best wishes 27th March 2018 From India