I just completed my house in E-11 and shifted last month Allhamdolillah. First, do not go other than E-11 or second choice as D-12.
E-11 prices are really high. No one expected that E-11 will rise so much. Honestly, Still can't understand why prices are so high. Reason in my mind, location and no other posh sector available. 1 kanal plots are a lot in number especially in E-11/3. Some other reasons but answer will get long.
E-11/3 is best sub-sector but you will not be able to find plot in this budget. E-11/2 is also good but some areas like Medical Society is at very low height. E-11/1 multi developed is also good. E-11/4 is mix, depends upon location. I also live in E-11/4.
You can go for D-12 too. It will take time to develop but would be great once developed. It's close to E-11 and closest to Margalla Hills.
Do not go for G-13 if you have budget. G stigma is very strong in Islamabad. Though ethically it's wrong and stupid, but we can't beat perception. Even if you go for G sector, better to go for G-15 and get 75x120 plot I.e 1000 sq Yard. You can have good lawn in it.
If interested in more information, let me know. If you are coming on Eid, you can visit E-11 and meet if interested.