GitHub Copilot is the strongest fit here because it integrates directly into the pull request workflow on GitHub, can review diffs for bugs, suggest fixes, and flag unclear code with inline comments where developers already work. It understands context across files and is purpose-built for code quality tasks rather than being a general assistant. Deepseek Coder is a solid free alternative if you want to paste code snippets for review outside the IDE. Claude Sonnet handles nuanced reasoning about code clarity and edge cases better than most when you need a deeper explanation of why something is buggy.