My first AA was basic m4 upper with standard polymer handguards. I upgraded to Danial Defense 7" omega rail and thought it was very well balanced. Think about it for a moment. The weight if heavy compensator or variance of weight from different buttstocks affects balance much more than the 2 extra ounces or so added mid barrel by the piston components.
My second AA was a custom I built on an 18" stainless WOA rifle length barrel with a rainier arms xtc comp and troy's top rail only freefloat tube. It shot like a dream with minimal recoil pulse. Very accurate.
My next AA upper will be the midlength evo ultralight or similar. Ive always shot pistons with an H2 buffer and been very happy. Ive shot many none AA pistons as well but I come back to the AA for lower cost and flexibility of non-proprietary rails.