both will provide virtually identical performance. that being said, DONT get systema barrels. from my experience, they have sucked. yes, they are an improvment over stock barrels, but stick with good brands, like Prometheus, PDI, Madbull and KM. Here is a breakdown:
PDI: Makes 6.05 and 6.01 (get the .05 for accuracy and the .01 for fps increase). personally, i would avoid these barrels just cause they are really pricey and you can get another barrel from another company that will perform just as well if not better.
Madbull: (6.03)relatively new to the barrel scene, but are tried and true. Most of the people i hear talk about them like them.
Prometheus: (6.03) For the vets at my field, this is the bread and butter of airsoft accuracy. If you buy one of these, rest assured that you are getting the best performance and accuracy for your gun
KM: (6.04) Ive mostly seen this company make pistol barrels. They also make AEG inner barrels. I just bought one for my Tanaka Kar98k. The reviews i have read for them have been positive. From what i recall, they are solid performers with accuracy compared to Prometheus barrels. IMHO, i get these when i cant find a prometheus barrel for my gun. case and point, my Tanaka Kar98k now has one of these (once it is installed that is
)
hope that helps!