See Man I had tested all three map one by one as given below.

1. City Navigator India NT 2010.20 (70 Cities)
2. City Navigator India NT 2010.30 Beta (428 Cities approx. idea but not because i got this news from Garmin)
3. Garmin MapmyIndia- Satguide 620 cities MMI v4.01
4. OneIndia Satguide INDIA STREET MAP 628 Cities Map update 28April10 -Garmin

And I found that Garmin MapmyIndia- Satguide 620 cities MMI v4.01 is best detail coverage but not able to find pin code of some city.