It's been a while, but last time I checked, write latency on R2 was pretty horrendous. Close to 1s compared to S3's <100ms, tested from my laptop in SF. Wouldn't be surprised if they made progress on this front, but definitely do dig deeper if your workload is sensitive to write latency.
Another (that probably contributes directly to the write latency issues) is region selection and replication. S3 just offers a ton more control here. I have a bunch of S3 buckets replicating async across regions around the world to enable fast writes everywhere (my use case can tolerate eventual consistency here). R2 still seems very light on region selection and replication options. Kinda disappointed since they're supposed to be _the_ edge company.