This type of question can be best answered by yourself only. What kind of job you want? To get selected for both you need to crack the entrance exams which are GATE and UPSC. Now, both have different job profiles and the post of IAS is obviously much more famous. But if you want to gain more knowledge and want to relive your college life with future scope, you can go for MTech. But make sure that to do your MTech from good colleges like IITs, NITs etc. You can also go for IIT JAM after BTech which is conducted for those who wants to take admission in the IITs for a bright career ahead. GATE is comparatively tougher exam then JAM. So, your chances do get increased to get admission in the top IITs.