The Bottom Line Up Front
All four tools can write cold emails. Claude and ChatGPT produce the best output. Claude is marginally better for quality; ChatGPT is faster for volume.
Test Methodology
We ran the same cold email prompt (trigger-based, personalized, under 120 words) through Claude, ChatGPT, Gemini, and Copilot. Each prompt included: company, prospect name and title, trigger event, suspected pain, solution in one line. Outputs were evaluated on: personalization quality, natural tone, absence of AI tells, adherence to word count, and reply-worthiness.
Claude
Consistently produced the most natural-sounding output. Strongest at weaving the trigger into the opening without sounding forced. Best at calibrating tone to the prospect's seniority level. Occasionally slightly longer than the word limit.
ChatGPT
Very close to Claude in quality. Slightly more formulaic openers but strong overall. Fastest response time. Best choice when you need to produce 15-20 personalized emails in a single session.
Gemini
Solid output, slightly more formal in tone. Works well but requires more iteration to get to a natural-sounding email than Claude or ChatGPT. Better with Google Workspace integration for sending directly from Gmail.
Copilot
Weakest for standalone cold email generation. Performs better when used directly in Outlook to draft and refine messages in context. Don't use Copilot for batch cold email generation outside of Outlook.
Verdict
Claude for quality. ChatGPT for volume. Gemini for Google Workspace. Copilot in Outlook only.