What is the closest fake diamond to a real diamond?

Can you tell me, in your expert opinion, what is the most convincing imitation of a real diamond currently available on the market? Is there a specific type of synthetic diamond or simulated stone that closely mimics the appearance, durability, and even the optical properties of a natural diamond to the extent that it could potentially deceive even a trained eye? And what sets this particular imitation apart from other less convincing alternatives?