headwork is going the more exspensive route but yeild power longer and more reliably. NO2 will indeed give a larger bang but its real easy to get gready with juice. a mistuned nitrous motor is a dead motor. a mistuned ported motor is a running motor that runs like ass.

weight your options wisely. I would always recommend headwork over nitrous for a street car. unless you're building a strip car KISS.