It all depends on what your really interested in!

Have a fixed mindset and a properly planned future in your mind always!

By the way, coming back to the question all the 3 fields have they own Pros and Cons

Mechanical Engineering is more about practical stuff and involves a lot of maths and formulaes. The Portion is quite outdated and no one uses the theory written in the textbooks. The branch is also quite interesting if you love cars and engines and how machines are madde and they run.

Computer Science is the stream which mainly complies of practical knowledge, how good you are at coding which is what matters the most, the more languages you know and the more websites or apps you have build is what will matter the most. Companies will hire students who have more practice and experience in coding. Only if you love coding choose this stream.

Civil engineers are hired in the organizations like real estate and construction, oil and gas, development authorities, and more. There are job openings in both government as well as private undertakings.

Mechanical Engineering degree can land you jobs at various companies and it will not limit your job opportunities to only mechanical engg oriented jobs. Many people work at various other type of firms.

Computer science degree will land you jobs in mainly corporates or you can opt for startups the pay is more than usual inexperienced fresher for an corporate.

Civil Engineering you can land in any of the sectors private or governement.

So, choose wisely.