Hello Soumyadip,

Yes ,it is true that Diploma is far better than ITI. Because ITI is a certificate course while Polytechnic courses are Diploma course. ITI are only skill development course that enrich your skill in various departments like welding, electrician or say wiring.
There are three categories of apprentice according to Candidate qualifications :-

• Trade apprentice : here either fresh candidate or ITI qualified candidate can apply
• Technician apprentice : here Diploma holders can apply
• Graduate Engineer apprentice

So Aspirant you can apply to the Technician apprentice according to your qualifications. This is due to the Indian railway Train apprentice under Apprentice act ,1961.

Hope it helps !