Hello!!!
Now according to your question it is really difficult to compare Mechanical branch over computer science, because both these branch are royal at there place.
But there is a common factor among these branches is you have complete interest in these two courses without this you will have to trouble to find job and clear examination is also a tough job at end.
Now if we are talking about the subjects in these two streams is completely different.
Were in Mechanical branch commonly you have to work in fields workshops, required physical with mental stability also whereas on other side computer is the branch of skills mainly.
Computer science required only mental focus and less physical fitness. Or physical fitness is secondary thing.