Delhi to Ahmedabad is a 950-1,000 km drive, & traveling time would be approx 16-17 hours.
The best route to arrive in Ahmedabad from Delhi is: Delhi > Neemrana > Jaipur > Ajmer > Mount Abu > Patan > Ahmedabad.
Anther popular route to reach Ahmedabad from Delhi, passes through Udaipur. Here after Jaipur, we take the Jaipur Udaipur highway, and its mostly taken for those travellers who want to stop in Udaipur.
This 2nd route (that passes through Udaipur) is 1,020 km long & takes 17-18 hours to reach Ahmedabad.