it all depends on your need and every company has it's own especiality
Telenor (If you need very good coverage in almost all the areas of Pakistan)
Zong (If you need very good internet speed coverage is good in northern areas but cities main kabi kabi masla hta hai but call and SMS quality is bad)
Jazz and Warid (Pathatic in coverage and rates)
Ufone (Call rates are good, call and sms quality are good but internet is very bad)
SCOM (if you are a traveller very high quality call, SMS and internet but very very expensive)