Which engineering is better -mechanical or aeronautical ?
Both are good. However, if you have decided and focussed on a career only in the aero field then aeronautical could be a good choice. If you are undecided and want to keep your options open till you complete graduation, the mechanical engineering could be a better choice. Taking mechanical also opens up specialisation in different fields after graduation, like aeronautical, automobile, robotics etc.,
If you take a specialisation directly after 12th, your scope is narrowed to that particular area, while taking a general and broad course like mechanical gives you a wide choice. Also, the interests towards a particular field may change in the next 3-4 years, and hence keeping options could be a wise move.