Hello Aspirant!!
Mechanical branch is mother branch of all engineering stream and it has large number of scope.Cse is also one of branch of engineering where engineers almost paid more than any other branches for the same institute.Actually packages are very high for CSE engineers as compared to mechanical  and there are large no.of opportunity for CSE branch in current market.For mechanical,if you have to qualify gate exam with good rank for getting high packages in best psu's.So,both of branches have its own value.
Hope it helps!!