Long-form blog posts (1,500-3,000 words)
Winner: Claude Opus 4.5. Most natural-sounding prose by default; less prone to AI-ish patterns like over-bulleting and excessive transitional phrases. Writes longer cohesive sections without losing thread.
Second: GPT-5.2. Faster and more confident; sometimes overconfident. Good for first drafts you'll edit.
Skip Gemini for pure blog writing unless you need long source documents — its prose is competent but rarely the most natural.
Marketing copy and ad creative
Winner: GPT-5.2 for variety, Claude Opus 4.5 for brand-consistent voice. The choice depends on whether you need 20 angles (GPT) or one carefully-toned line (Claude).
Specialist tools (Jasper, Copy.ai) outperform general models on templated marketing assets at volume, but require subscription on top of your general AI. For under 50 marketing assets/month, a general model + custom prompt is usually enough.
Technical writing (docs, runbooks, API guides)
Winner: Claude Sonnet 4.5. Following instructions precisely matters for technical writing, and Claude leads on that axis. Less likely to introduce unsupported claims.
GPT-5.2 Codex is also strong specifically for technical content with code samples.
Editing and rewriting existing copy
Winner: Claude Opus 4.5. Better at preserving the original author's voice while making the requested change — single most common complaint about AI editing is 'it sounds like a different person now'. Claude is least guilty of this.
Brand-voice work (consistency across many pieces)
Winner: Vincony Brand Kits (Business tier) with Claude Opus 4.5 under the hood. The Brand Kit feature stores your voice rules and applies them automatically to every Claude completion. Without the wrapper, manual prompting is workable but inconsistent.