A while back I gave the same task to both, and Codex used 20x less of my 5-hour limit (both on the $20/month plan).
(This annoyed me since I tend to prefer Claude, but the limits at the time made it unusable for anything serious.)
However, since that time, both providers have massively reduced usage allowances (and at least one of them has gotten sued for it, lol).
I'm not currently subscribed to either but I'm weighing my options. With GPT being slightly better than Opus, and it used to have way higher limits, I'm leaning in the direction of an OpenAI sub. But I'm wondering if the current state matches my memory from 2-3 months ago. (Since both companies appear to be cost-cutting hard!)
Prefer responses from people who use both, but anecdotes welcome :)
Thanks!