Originally Posted by tx787
if you want an AR get DI and just keep it clean and you won't have any problems.
Actually, just keep it lubed
and you won't have any problems. One of the most common misconceptions regarding the AR platform is that they must be clean to be reliable. It just isn't true. A very dirty rifle will run reliably as long as it's wet.
To answer the OP:
A piston on an AR replaces one standard reliable part (gas tube) with several non-standard proprietary parts, more parts with the potential to fail. It also add weight out front where it's very noticeable. Carrier tilt can also an issue with a piston.
DI ARs are as accurate as they are with little felt recoil and muzzle rise because of the in line nature of the barrel, bolt carrier, and buffer/spring. Adding a reciprocating piston above the line of the bore negates this concept as designed.
A piston AR may be cleaner, but as I mentioned ARs don't need to be clean to be reliable, so it's really a solution to a non-existent problem.
These are my thoughts, YMMV.