I keep travelling between the two metros almost every alternate month and hence frequently travel through Rajdhani. Main Rajdhani (Delhi-Mumbai) , starts from New Delhi station where as August Kranti Rajdhani starts from Nizamuddin, despite taking same amount of time, belonging to same organizations, same fare, the two trains are highly different in terms of their services.
Rajdhani is more punctual compared to August Kranti, though the major difference comes in their staff. Services in August Kranti are much slower compared to main Rajdhani, also staff is not all that supportive as one can experience in main Rajdhani. Though getting reservation in Auguist Kranti is relatively easier, if one has the choice between the two I would recommend Main Rajdhani unless one has to get down to Borivali (Main Rajdhani doesn’t hault at this station). It has never let me down both in terms of running on time and staff services, to me it is a highly recommended value for money train service