Sequoia aims to be a "complete gnupg replacement" but in many ways it's still the same mindset as gnupg (core devs are former developers of gnupg). Sequoia also got support from VCs and just recently received significant funding from the STF which gives them resources to polish the documentation etc.

Rpgp is much smaller but also very flexible. It's easy to adjust to more specific needs. It's also associated with RustCrypto project and with Rust in general.

For example to add rpgp to your project you just do "cargo add pgp". To use Sequoia "properly" you need this multiline setup which depends on whether your crate is a "leaf" crate or not: https://gitlab.com/sequoia-pgp/sequoia/-/tree/main/openpgp?r...

Another example: Sequoia is against rustfmt. This makes it harder to contribute.

On the other side rpgp is much more barebones and instead of docs you need to read the source (which is rather readable).

Both of them would benefit from a high level API, so that the users wouldn't have to work with types such as ValidUserAttributeAmalgamationIter (https://docs.rs/sequoia-openpgp/latest/sequoia_openpgp/cert/...).

Full disclaimer: I've worked 3 years on core Sequoia and I'm kind of involved in the OpenPGP protocol: https://github.com/wiktor-k