Why is Arbitrum better than Optimism?

Could you elaborate on why Arbitrum is purportedly superior to Optimism? It seems both platforms employ Layer 2 solutions to enhance Ethereum's scalability and efficiency, yet there must be some distinguishing features that give Arbitrum an edge. Is it the security mechanisms, the transaction throughput, or perhaps the cost-effectiveness that tilts the scales in Arbitrum's favor? Additionally, how does Arbitrum's compatibility with existing Ethereum ecosystem factor into this comparison? Understanding these nuances would greatly assist in appreciating the nuances between these two platforms.