The best blockchain for building an Augur clone depends on what you value most like cost, speed, and scalability, but in simple terms many developers still choose Ethereum because the original Augur was built on it and it offers strong security and well-established smart contracts, however for a modern Augur clone script most projects now prefer faster and cheaper networks like Polygon, BNB Chain, Arbitrum, and Optimism because they offer low transaction fees and better speed which improves user experience in prediction markets, so if your focus is security go with Ethereum, but if you want more users and smoother performance then Polygon or Layer 2 solutions are the better choice for your Augur clone script.