Rifled barrels are only worthwhile if shooting shaped rounds like First Strike from a magazine fed gun. With regular paint they won't make any positive difference, if anything they can make matters worse. Flatlines can be ok but they mostly pointless, inflexible and can be more hassle than they are worth. The only 'trick' barrel I've seen of any worth is the Apex 2 as it's highly adjustable and the effect can be turned off. But you'll still burn though a heck of a lot of paint trying to pull off those crazy shots and unless you've got a Freak version don't expect much consistency as the standard Apex 2 barrel is as wide as a drainpipe.