Dear Khan,
Nafees means to email me as i rarely check forum (issues with zameen admin and policies) but always available on email if i can help i will. BTW is started by Nafees too he was giving my email to others. Bhai Nafees kabhi khud bhi email kar liya karoo humain.
To your question, you choose well. Block 15 is most peaceful area but water problem. Load shedding 1 hour 3 times a day. Also its most away from Nipa (if we consider it our main traveling point), Range??? 130 to 145 depends on location, condition, stories etc etc. The area behind the Darul sahet hospital is most secure .i.e. all house of same cutting, barriers and guards in every line total residential but you got other option too as its pretty big block. About block 10-A good but not the best as very confused cutting there so many places. Security wise don't see except near erum bungalows.
Water and load shedding as block 15. Here you can get from 120 to 140 same factors. Now come to 13-d the most interesting choice. From one side is very best (the part touching University road but worst in area facing essa nagri also the back of 13-D. Range varies and varies so much. No organized security. Don't know water and electricity situation there. Need to know your preference so suggest better. Why don't you check in block 5 and 6 of Gulshan as well??? Waisay bhi dost Karachi main security kahan ab tu Defence bhi safe nahi raha aur jo area i can really say secured its not for civilians. Recently two more join from Karachi here (@A and @FooBar) contact them too. It's better to get more opinions may be i missed something which they can tell you.