See both the ways are good. If you want to go for a elementary knowledge in Engineering before going into BTech then you can go for Diploma in Engineering although in many cases student faces various problems due to the lack of knowledge in Physics and Mathematics mainly calculus. So if you wish to go for Diploma in Engineering then you should be very sincere about your first year because in that year you used to learn this tools which will be required laterwards. Now after your diploma you can get jobs although the jobs aren't that good compared to BTech but still it has possibility. Also after Diploma via lateral entry examinations you can go for BTech and get admission in the 2nd year of BTech directly. But in case of 12 you will not be able to get jobs and other facilities but after 12 you get more options to choose. You think of engineering and while studying in 12 you find that physics is not your thing so you can go for other engineering fields or non engineering field.

So its on your wish ambition what you want to take. After 12 also there are great engineers and after diploma also there are also good engineers. So based on your interest you have to choose the way.

To know more about Engineering courses visit the link below:

https://www.careers360.com/courses/engineering-course

I hope this answer helps. All the very best for your future endeavors!