I want to buy flat in sec 4 or sec 5 or sec 12

Buying your own house is a big decision and you don't want to compromise on location. I can understand your situation, finalizing the perfect location is also a major task. But don't worry here I have explained the pros and cons of all three locations so that you can choose which suits you the best. 

Sector 4 is a residential area in Old Gurgaon. In this location you will find mostly independent houses and builder floors. This location has excellent connectivity as it is located along

the Old Railway Road, Rezang La Marg and Dhanwapur Road.You can also travel via metro and the nearest metro station is MG Road Metro Station.

You can find premium schools here such as

Jiwan Jyoti Senior Secondary Public School, St. Michael's Sr. Sec. School, Blue Bells Model School, Government, Senior Secondary School and Arya Vidya Mandir Senior Secondary School. And healthcare hospitals are also located in this locality. 

You can also find employment huns near the boundaries of Gurgaon Sector 4 located within 10 kilometers from the location such as Unitech Infospace Complex,Udyog Vihar and Cyber City. 

This residential location is closely located to Gurgaon Sector 4. In Sector 5 you can find independent

houses and builder floors. Gurgaon Sector 5 comprises few housing societies with low-rise buildings. You can travel via metro as MG road metro station is just 5 kilometro away from the location. You can also travel to other parts of Gurgaon via Old Railway Road and Sheetla Mata Road.

You can find famous schools around this location are Open Sky School, Aakash Public School, GAV Academy, Xion International Convent School and Mother's Pride.

Gurgaon Sector 12 is a residential hub and is also famous for its old car market. You can find many premium schools in this locality such as Ajanta Public school, GD Goenka World School, Kamla International Public School.

The average property rates in Gurgaon Sector 12 are between Rs.

8210 and Rs. 9820 per square feet.

I would suggest taking a tour and doing your own research for the best locations you are looking for. I tried to explain the highlights of all three locations but I might have missed something that you check in the first place when it comes to buying a property in a specific location.