Pulsar is more flexible and fault-tolerant. For me the most important thing is client can request log queue starting from specific log by id, it has better retrying mechanisms for logs that failed to be processed. But it has absurdly bad documentation. I had to learn many things about Pulsar by downloading src of their java library and just reading the code. Documentation on starting bookie, zookie, pulsar, pulsar-proxy cluster was non-existent, and making it work like in their architectural diagram was a week of work and experiments, compared to literally 2 hours spent in Kafka.

Bookkeeper has/had even worse documentation and setup. When I used it bookie couldn't have mounted directory for log storage, so it's not really that persistent as they say. Before restarting bookie node it has/had to be reformatted to allow bookie instance to re-use logs saved on disk. The whole "log are persisted" is true, but they don't say that you can't simple mount them in docker and restart your PC to it.

Pulsar is good when you get it working. Documentation is really bad and it's hard to make it work. All the super-positive articles about pulsar are sponsored (streamnative and yahoo) and biased to make pulsar look much, much, MUCH SIMPLER than it actually is.