As a career PSP is better but when it comes to power and contacts, nothing beats FIA. As a ASP in a police station you would deal with criminals/murderers and lowest strata of society but as AD in FIA you would be investigating crimes of much bigger nature involving the elite, case in point recent NICL/Moonis Elahi fiasco. My father was an AD in FIA and each and every case he handled involved big shots, including Sharifs, Bhuttos, Presidents of Banks etc. He also arrested several politicians. Can you imagine a ASP or SP doing this? This isn't even their domain.