I've got a PWS conversion that is on a Saber Defense 16" upper, love it. I think if I were going after a new system or complete rifle it would be either the Ruger SR-556 or if I were willing to keep saving, a LWRC.

As others have noted the recoil impulse is different. I personally don't think it's heavier or any more tiring than a DI weapon. It's hard to describe accurately the difference. Either way, its something you'll notice if you're swapping between a DI and Piston gun in the same range trip or class, but not really anything you'll notice if you're only running the piston gun.

Look for a piston system that keeps most of the retaining pieces captured. The PWS has a small guide pin that I've spent some time finding again and some "I"m an idiot" moments making sure it's seated correctly during re-assembly. The LWRC, Ruger and Adams Arms systems seem to better capture all of the little pieces.

Still a fantastic improvement to the AR system, while I'm not trading out the other DI AR's I have, the PWS is by far my favorite.