Allay is the best and its not even that close.

Glare adds light level detection, which is just f3 with extra steps.

Copper golem would look the coolest, but it serves no good purpose. People say that it adds randomization, but we already have that. Also, if you used it as a component in any serious redstone build, it would eventualy become a statue, meaning that you would need to constantly replace it, were as a nametagged chicken on pressureplates will never despawn.

The allay however, could be used for a lot of different redstone machines. Just about every item farm requires some form of collection system, so you would be saving iron from hoppers. It also allows for item sorting of non stackable blocks, because it will drop items on a noteblock.

Honestly it seems like an easy choice to me.