Robustness and efficiency of consensus protocols

What are the most robust and efficient methods to establish consensus in a blockchain? Nakamoto Proof-of-Work is the most established blockchain protocol, but attacks on low-hashrate chains like Bitcoin Gold have shown that hashrate marketplaces can present a serious threat. Proof-of-Stake is a common alternate proposal that reduces the energy requirements of the chain but typically induces significantly greater complexity. Additional questions include how to handle congestion when writing data to a blockchain, and associated strategic behavior (e.g., collusion between users and miners).

Professor David C. Parkes - "We look closely at the rules that define crypto-economic systems and try to understand their incentive mechanics. We have found profitable, dishonest strategies that deviate from the defined protocol in both the Tezos and Ethereum 2 Proof-of-Stake systems. With the rise of Decentralized Finance (DeFi), we are now exploring the design of well-established projects such as Uniswap v3."