Gulberg green, taj residencia, or 18
I will prefer Gulberg Greens, the development is already done, the access is very good, commute time to Islamabad and Rawalpindi areas is better and its way ahead of other two options which still needs to be developed.
18 is also located on the one of the best location but its expensive option. Moreover its years behind in terms of development as compared to Gulberg Greens.
Taj Residencia is not any where near both in terms of access and infrastructure as compared to other both options.
I see another Emaar Canyon View sort project in 18...
With location Taj is too expensive, no matter even if they promise some Centaurus or Burj 2 sort thing there
Gulberg is fine, Greens is saturated, Residencia was among one of the best appreciating project that got a bit slow recently but still has charm both for end buyers and investors. Gulberg being a cooperative society is dead slow in comparison to its main competitors. Go for possession or near to possession ones with plot on ground and numbered, dont fall for files thing
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Pls. Read above as totally personal views, opinion and perception rather than some definitive facts in favor or against other.