Shimano for the best shifting on Shimano groupsets, always just seem that little bit smoother & slicker, but not ass reliable as I’d like (snapped one or two..)
Personal preference is KMC, for both road & mtb.
Shimano chains are made by KMC
That may be true, but only in the same way as Colnago frames are made by Giant-same factory & same employees, but very different products.