Whether a Diploma in Aeronautical Engineering is better than a Diploma in Mechanical Engineering depends on your career goals and interests. Both fields are valuable, but they cater to different industries and career opportunities.
A Diploma in Aeronautical Engineering is very specialized in nature and involves designing, maintaining, and operating aircraft and spacecraft. This diploma will be a good option if you have a passion for aviation, aerospace, or working with advanced technologies in flight systems. The opportunity is in airlines, aircraft manufacturing, defense organizations (for example, DRDO, ISRO), and research institutes.
A Diploma in Mechanical Engineering is more diversified, covering areas like automotive, manufacturing, energy, and robotics. This offers greater scope for different types of career and flexibility in shifting between industries.
A specialized career in aviation would be better for aeronautical engineering, but if you wanted to have more opportunities and options within industries, then mechanical engineering would be the better option.