The Glare:
The Glare's purpose can easily be recreated using a Vanilla feature: texture packs

The Allay:
has a purpose, can stack non-stackable items and will be the 1st mob that can help you with Redstone

The Copper Golem:
The Copper Golem doesn't have a purpose other than the fact "it looks cool". It probably randomly presses buttons so it'll be inefficient for Redstone farms and it stops pressing buttons once it oxidizes. Basically another useless use for Copper.

therefore the allay is superior because it isn't actually an item duper like most people think it is.