I guess your a DI guy. i have actually been looking into both. but i herd the piston has a little more wieght up front so you misght be able to stay on target a little easier. but the di wieghs less so u can swing it around to target better. I know the bolt carrier stays cleanier and cooler on the piston but the di has no carrier tilt problem.
whats your opinion on the pros and cons of the two?
I really don't know that much about the gas piston AR's to be completely honest. What I do know is that I shoot a lot of 3 gun competitions and these competitions put the AR through a lot of use and abuse. You don't win without a good reliable rifle and I don't see piston driven AR's taking the place of any DI rifles. That is the sole reason I wouldn't buy one. If you look back at the optics and rifle systems the military adopts a lot of those cool new items are spun out of the competitive shooting scene.
If your heart is set on a Piston AR that CMMG that Olyeller has is a great buy with no taxes on a brand new rifle. I fondeled it the other day when I was picking up a pistol and liked what I saw.