Till Last Year, Admissions to Delhi University were purely based on Merit (Class 12) and No Entrance Exam was conducted for Majority of Colleges. However, certain Meritorious Colleges like St Stephens, call the shortlisted students in Merit List for an Aptitude Test and Interview. This Year however its unclear, how Delhi University will proceed with its Admission and Counselling Procedure with Std 12 Board Exams getting Cancelled.

For more information regarding Delhi University Admission do follow the link below

https://university.careers360.com/articles/du-admission/amp

Coming to the second half of your Question, I believe for Graduation Delhi University is the Best in India, having excellent faculty, infrastructure, alumini network, career scope and prospects with some of the best meritorious students and high cutoffs.

DU is followed by JMI, then BHU and lastly AMU if you consider the Infrastructure and Faculty  as well as Campus Perspective. However, the education imparted and curriculum is equally strong in all the above 4 Central Universities.