Eisha M. answered 10/11/20
Native Urdu Speaker who has aced O Level Urdu
Delhi Urdu is closer to Lucknowi Urdu. Lucknowi Urdu was historically purer and Delhi's was considered corrupted. However in present times it is difficult to find people, at both places, who speak any kind of Urdu; let alone the pure form. Today, Delhi Urdu and Lucknowi Urdu sound practically the same.
The Lucknow/Delhi Urdu is derived directly from 'Hindustani’ wherefrom Hindi too is derived so the accent is similar to Hindi.
While the Hyderabadi Urdu is called 'Dakhini Urdu’ which includes some Marathi, Kannada and Telugu words too and the accent is a mixture of accents of people who speak these languages.
Marathi is derived from the older language Maharashtri which still shares the 'Prakrit’ base with Hindi. But Kannada and Telugu are not a part of the Vedic Sanskrit derived language tree at all. Which is why Hyderabadi Urdu(Dakhini Urdu) sounds substantially different from Lucknowi Urdu(Urdu of Avadh).
Side note - ‘Dakhini’ comes from the Urdu word Dakhin/Dakkhin/Dakhan/Dakkhan(The Hindi word for which is Dakshin) which means 'South', and ‘Dakhini' means 'belonging to southern India'. It must be noted that the word Dakhini, although can now be used in a more general sense, originally meant and usually means 'belonging to southern India' and not 'belonging to south'. The usage is this specific because the language Urdu was born and evolved in India and was spoken only by the people of this country, and I am assuming that the need for referring to things and people from the southern part of their own country would have been more pressing than referring to anything further south.
Fun fact - The 'Deccan' in ‘Deccan Plateau' is the anglicized form of 'Dakkhan'.
Source: Quora