Hard-sided or soft-sided—which is better for a cat?

It depends on the trip. Across r/CatAdvice and r/CatsUK, reviewers favor hard-sided crates for vet visits and car travel because they don't 'cave in' and are easy to disinfect, while structured soft-sided bags win for flights because they squish under seats. The recurring advice is that soft carriers still need a rigid base and some sidewall structure so the cat isn't squashed.