Codex with GPT-5-High is extremely good. Like many I was a bit "meh" about the GPT 5 release, however once I started using it with Codex it became clear there was a substantial improvement in a capability I wasn't really paying attention to, which is tool calling. Or more specifically, when to call a tool. Ask GPT-5-High a question about your codebase and watch the things it looks for, and things it searches for (if you use --search). It has very good taste on how to navigate and solve a problem.