As per census 2011, Gurugram (Gurgaon) has the highest population among the four cities mentioned in the question. The population of Gurugram in 2011 was 10,54,921. The population of Gurugram is expected to be 17,33,982 in 2020.
Ambala had a population of 5,62,037 in 2011 and is expected to have a population of 7,34,611 in 2020.
Panipat had a population of 3,71,116 in 2011 and is expected to have a population of 4,85,829 in 2020.
Faridabad had a population of 17,88,095 in 2011 and is expected to have a population of 24,53,748 in 2020.
The population of Gurugram is expected to grow at a faster rate than the population of the other three cities. This is due to the fact that Gurugram is a major industrial and commercial center in Haryana. It is also home to a number of educational institutions and hospitals.