I used idea network for almost 2 years and found that idea network in Delhi is pathetic as well as tgey was having only 2G ( Recently launched 3G while its time of 4G).
Yes network coverage of idea is good in UP and haryana but Delhi, pleas dont ask. If you buy idea netwotk in Delhi then you have to go to your roof top so that it can show you 2-3 bars on your phone and you can make a decent call other wise disturbance and going to rooftop in summers think about it. Please dont buy idea if you are in delhi.