I will leave you with this... and will let this horse die...
Larry Vickers said the following on M4C.net:
"Piston AR's have their place- to determine if you need one ask yourself four questions;
1) Do I need a barrel length shorter than 14.5 inches
2) Do I need to run my gun suppressed a lot
3) Do I need to shoot a lot of full auto
4) Do I need to shoot a wide variety of ammo
Piston guns have been shown to be superior in those four categories over a DI gun. If you can say no to all four questions a good DI gun will do you fine.