Is Ethereum better than Arbitrum?

Could you please elaborate on the comparison between Ethereum and Arbitrum? Which platform offers superior scalability and transaction speeds? Are there any significant differences in terms of security and decentralization? Also, how do the costs of transactions compare on both networks? Could you provide insights on the developer communities and ecosystem support for each platform? Finally, which one do you consider to be more suitable for specific use cases, such as decentralized applications or token issuance?