I don't know about Aider, I am not using it because of lack of MCP and poor GitHub Copilot support (both are important to me). Maybe in the future that will get better if that will be relevant. I am using opencode.ai with Claude Sonnet 4 usually. Sometimes I try to switch to different models, e.g. Gemini 2.5 Pro, but Sonnet is more consistent for me.

It would be good to define what's "smaller code bases". Here is what I am working one: 10 years old project full of legacy consisting of about 10 services and 10 front-end projects. As well tried it on project similar to MUI or Mantine UI. Naturally on many smaller projects. As well tried it on TypeScript codebase where it has failed for me (but it is hard to judge from one attempt). Lastly I am using it on smaller projects. Overall question is more about task than about code base size. If the task does not involve loading too much context when code base size might be irrelevant.