dns in nautical science is better or btech. in marine engineering is better????

Hello, Both the courses are very different and there can be no simple comparison. Instead you must try to figure out which course is the best fit for you. You can do that by going through the syllabus of both the courses, exam pattern and job prospects. Also, don't take any decision in haste, because once you choose a course, you will be linked to it for the rest of your life. Think whether you want to pursue one of these two courses just because a friend of yours is doing so, or you are really passionate about it. In fact passion is important, because it will motivate you to work hard in your chosen discipline. Best of luck.