I'd say it's more of an opinionated approach to a web framework, which reduces boilerplate on a lot of simpler applications. In order to facilitate this, it ends up creating more of a Domain Specific Language (DSL) using macros and types for Rocket, which can be harder to manipulate in ways you might expect as a Rust developer.

Axum on the other hand tends to avoid macros and uses the type system in "more composable" way with other Rust crates, and while still providing a concise way to create web apps, has resulted in more boilerplate to hit the ground running in my experience.

*axum I migrated a rocket project to axum 1~2 years ago, due to rocket being dead at the time. Both frameworks contain all you need to build an API really. But personally I found that: Rocket is easier for beginners, and once you know what you're doing, Axum is cleaner and better integrated in the ecosystem.

It probably feels more familiar if you are coming from the world of Python’s Django or Flask. Other than that Axum is very likely a better choice for all use cases.

There isn't one, I migrated to axum and won't go back.