It's really up to you. I own more piston ARs than I do DI. My go to though is a KAC SR15. It's just lighter so at day long carbine courses it makes it somewhat easier.
There really isn't a right answer. Both will serve you well. For those that say it's more parts do the math.
Maybe a spring
I would bet that the gas rings or tube will go bad before a op rod, piston or plug.