I hate when someone says THE BEST on such a vague topic. N/A as in no forced induction, possibly nitrous? What heads? How much compression? Stock short block? Built? Specs on built engine if so? What's your whole intake setup look like? What are you running for an exhaust? What are your power goals? What do you intend to do with the car?
That's just some of the basic shit. Otherwise, look into Hitech stage 2 cams if you have stock heads. A ton of people have had awesome results with them. There's an N/A 2 valve 4.6 that made it into the deep, deep 12s with them, bolt ons, gears, and some minor weight reduction. It was still for the most part a full weight street car.
YN Silver '01 GT - Main money pit
Black '01 GT - Racecar
'92 E36 BMW 325i - $500 daily driver
'86 Camaro - Sitting in a shed torn apart
'13 Kawasaki ZX-6R - Sold, too fast, want a Harley
'11 E92 BMW 328i xDrive Coupe 6MT - Daily luxury