Claude Code, where it can use tools and iterate; if it makes mistakes it will know as well and retry, this is a massive boost from copy pasting into chat and getting the trust broken by the LLM confidently making mistakes. By having it be responsible for the results, it has increased utility. E.g. "when I run the program I get error X, see if you can find out what caused it. Run make in ./build and run the program to see if the error is gone". In addition, Claude has written some nice code on occasion that was simply no different that how I would have done it. In a few sentences I can explain my coding style and the rest is derrived from existing code.