[Turbowned]

Well, here's the result you'll get with each:

Springs: pros: looks better, corners flatter
cons: shocks were matched to stock springs, car will now be oversprung and under-damped. Reduced ride height means you gotta watch out for those low curbs, dips in the road, and all that crap

header/OFT: pros: moar power! If you like it (I don't personally), more pronounced boxer rumble
cons: assuming you're removing both factory cats, your car's gonna stink like shit for anyone who drives behind you. It's gonna be noisy; watch out for cops

wheels/tires: pros: better looking than stock wheels, more grip for faster cornering
cons: car will be less tail-happy (if you enjoy sliding it around), reduced tire life (assuming you go with a high performance summer tire)