Hello student diploma degree and B.tech degree are completed different of two different level after pursuing diploma you can join as a junior engineer but after completing B.tech you hold a degree of Engineer.

Depending upon the eligibility criteria if you're eligible for B.tech then B.tech is more  preferable than diploma.

To get admission in top engineering colleges like NIT's IIITs CFTIs IITS and many others college you need to appear in jee main entrance examination
Eligibility - Candidates must passed or appearing class 12 with physics chemistry and mathematics with minimum 75 percent marks aggregate from a recognized board.
Feel free to comment if you have any doubt
Good luck