im asking a similar question in a different thread.
and as i posted, IMO mind you...
there is no real advantage gain one over the other.
DI is dirtier than the Piston but if you keep your stuff clean then it a non-issue. i have cleaned an AR that was SOOO gummed up with carbon, and IMO too much lubrication, that you could not charge the bolt without forcing it to the degree that made me cringe with the possibilities of things breaking
i just want to try out the piston for poops-and-giggles, as something new, and im looking retro-fit kit since i dont want another
though the piston does have the advantage the suppressor crowd and the clean factor, the DI has the advantage of SUPER easy to find parts, cost, and a proven operating system on the AR platform, while the piston is still somewhat of a new trick for a getting to be
my point... whats better or recommended? i would say for the easy of parts, cost, and PROVEN operation i would go DI,....but i dont have any real time experience with the piston so.... *shrugs*