Also while not quite as smart, it's a better pair programmer. If I'm feeling out a new feature and am not sure how exactly it should work yet, I prefer to work with Sonnet 4.5 on it. It typically gives me more practical and realistic suggestions for my codebase. I've noticed that GPT-5 can jump right into very sophisticated solutions that, while correct, are probably not appropriate.
Sonnet 4.5: "Why don't we just poll at an interval with exponential backoff?"
GPT-5: "The correct solution is to include the data in the event stream...let us begin by refactoring the event system to support this..."
That said, if I do want to refactor the event system, I definitely want to use Codex for that.
Moving a bunch of verbose templated HTML around while watching results on a devserver? Haiku all day. It's a bonus that it's cheaper, but the real treat is its speed.
Adding a feature whose planning will involve intake of several files? Sonnet.
Working specifically on 'copy' or taste issues? Still I tend to prefer Opus here.
Individual experiences may vary!