Claude Sonnet is the strongest choice for tailoring a CV and writing a marketing application letter because it excels at nuanced, persuasive long-form writing and can adapt tone and content to match a specific job description with precision. You can paste the job posting alongside your existing CV and ask it to rewrite bullet points, highlight relevant marketing skills, and draft a cover letter that speaks directly to the role. ChatGPT is a solid alternative if you already have a Plus subscription and prefer its iterative chat style for refining drafts. Claude Opus edges ahead on depth and sophistication for particularly competitive applications where every word counts. Jasper is worth considering if you want a writing-focused tool with built-in marketing templates designed specifically for professional copy.