What is Ethereum's biggest rival?

Could you elaborate on what you consider to be Ethereum's biggest rival in the cryptocurrency space? Are you referring to a specific blockchain platform that offers similar functionality, such as smart contract capabilities and decentralized application development? Or are you thinking about another cryptocurrency that aims to compete with Ethereum's market position and adoption? Additionally, how do you measure the success of a rival, and what factors do you consider when evaluating their potential to pose a significant challenge to Ethereum's dominance?