Since this is an HK site, obviously a lot of people here are going to be attracted to the 416 simply because of the brand.
As for the "superiority" of a piston AR over a standard direct impengement (DI) AR, a piston system runs cleaner since the gas is trapped in the gas piston assembly instead of being blown back into the bolt carrier and bolt like with the DI system. In therory it's a little better and if my life absolutely depended on it on a daily basis, or was planning to running 10,000 rounds through it without cleaning, then it might be something that I might consider. But, I think for 99% of the civilians who own ARs, use decent ammo, and keep them reasonably clean, the standard DI system will probably be reliable enough.
You can also talk about the 416's sights, rails, stock, etc, but that's all furniture, and you can get all kinds of stuff for the AR platform.
I think the main draw for the HK fans is that it's HK.