I started with ChatGPT and actually switched back to it briefly last December thinking it was better. Over time I landed back on Claude for one main reason: it does a better job following my voice when drafting client emails and communications. It picks up my style without me having to constantly correct it.
One thing worth knowing if you're on ChatGPT — the default settings are very agreeable. It will tell you your ideas are great even when they're not. You have to deliberately adjust that or you end up with false validation instead of useful feedback.
Both tools are evolving fast so I wouldn't call it permanent. But right now Claude handles my writing tasks better and pushes back when I need it.