Short recommendation
Use both: GitHub Copilot as your primary in-editor debug assistant for fast stack-trace fixes and local edits; use ChatGPT for test-case generation, root-cause brainstorming, and reproducible fixes that need broader reasoning or cross-file summaries.

Why (decision criteria)
- Scope of the problem: single-file/syntactic or call-site bugs → Copilot. Multi-step reproducer, race conditions, vague failure modes → ChatGPT.
- Access to runtime/context: if the fix needs local runtime access (breakpoints, repl) Copilot (editor + local execution) is faster. If you need to craft tests, reproduce with mocks, or explore hypotheses, ChatGPT’s conversational reasoning shines.
- Privacy/budget: Copilot stays inside editor workflows (better for repo-first workflows; may require enterprise licensing). ChatGPT is more flexible for large conversational context but you’ll need to manage sensitive data and API costs.

Concrete examples and time-saving estimates (typical mid-level backend engineer)
- Typo / wrong import / simple off-by-one in a handler: Copilot suggestion + accept = bug fixed in 2–10 min vs 10–30 min manually (savings ~50–80%).
- Stack-trace triage (clear call site): Copilot’s inline completions and signature help often point to the likely null/invalid input within 10–20 min vs 30–60 min (savings ~30–60%).
- Reproducible failing test for an integration bug (database/serialization race): prompt ChatGPT to generate a minimal failing unit or integration test and a set of hypotheses. Expect 2–6× speedup creating a stable reproducer (e.g., 4–12 hr manual -> 1–3 hr with ChatGPT help).
- Complex root cause analysis (multi-service interactions): ChatGPT can synthesize logs, stack traces, and sequence diagrams into probable causes—often saving several hours of brainstorming and coordination.

Practical checklist (how to use in a session)
1. Reproduce locally. If reproducible quickly, open file/stack frame in editor and let Copilot suggest inline fixes. Test locally. If it works, commit small fix + test.
2. If failure is nontrivial to reproduce, copy sanitized logs/stack traces and ask ChatGPT: “Given these logs and service interactions, produce a minimal failing unit/integration test and 3 ranked hypotheses.”
3. Use ChatGPT output to write deterministic tests; iterate until test fails locally. Then use Copilot to implement the fix in-editor and refactor.
4. Add the new test to CI and document the fix in the PR description generated by ChatGPT.

Best-for / Avoid-if
- Best-for Copilot: fast in-editor suggestions, local fixes, small refactors, signature help. Avoid if you need cross-service reasoning or to craft a deterministic reproducer.
- Best-for ChatGPT: test generation, stepwise troubleshooting, hypotheses, PR notes. Avoid for one-line fixes where editor flow is faster.

When the right answer depends
- Budget: Copilot (editor subscription) vs ChatGPT (chat or API usage).
- Team size / workflow: larger teams with strict audit/privacy may prefer Copilot’s repo-integrated flow. Remote debugging across services favors ChatGPT for collaborative reasoning.
- Skill level & stage: early-stage unknown bugs → ChatGPT; late-stage tighten/refactor → Copilot.

Final recommendation
If you must pick one for day-to-day mid-level backend work choose GitHub Copilot as the default in-editor tool, and call on ChatGPT for test generation and tricky cross-service debugging. For quick trials, start with Copilot and escalate to ChatGPT when you need reproducible tests or structured hypotheses.

Compare GitHub Copilot and Cursor