I've used both and NATS is definitely what I'd pick starting out. RabbitMQ is great too, but its heavier and harder to configure. Federation is the killer feature of RabbitMQ that NATS doesn't really have (afaik?).
Edit: spelling
https://docs.nats.io/nats-concepts/subject_mapping#for-traff...
(for more detail check out this and the other YouTube videos on the Synadia channel https://youtu.be/WH55czo1BNk)