if youre on a k03, use oem
if youre on a k04, use s3
if youre on a bt, use rs4
oem and s3 have a wide spray pattern (s3 will work without a tune on a k03, but its pointless cause theyre the most expensive) and wont cause a black bumper, but the rs4 injectors spray a little different and WILL need a tune. imagine a normal wide spray from oem or s3 and cut it in half... thats how the rs4 looks when it sprays. it can put more fuel to the engine, but it will cause a black bumper too.
in short, the rs4 is a waste unless your motor is around 400hp+. go with the oem unless your motor is lightly tuned, then go s3. if you go with the rs4 and your motor isnt at or above 400hp, then it will just cause a black bumper and youll prolly lose hp if you had went with the s3.
hope that makes sense