[Ibby]

Depends on how you play with your SAW. I have a tightbore barrel on my TOP M249 and it increases accuracy a ton. If you want your SAW to work like a SAW should, stick with the stock barrel. It'll simulate a beaton zone like a real steel SAW would have, which is great for keeping the heads down of the troops you run into while the riflemen take them out. If you want a big heavy accurate AEG get a tightbore.
I switch between barrels depending on where I'm playing, terrain, etc.