Briefly on some shortcomings with Whisper. The main positive about it is that it is default in Ethereum and in production. It suffers from lack of scalability, and it's DoS protection mechanism is poor.
- Anonymity claims not rigorous
- Lack of machine-readable spec
- PoW bad for heterogeneous nodes
- no incentive to run a node
- scaling difficulties
Briefly on what Whisper looks like in practice with Status.
- Cluster with bootnodes, nodes, mailservers
- Partial relaying on mobile
- Lower PoW (isolated network)
- Mailservers: HA requirement and direct TCP
- (Topics and chat)
Whisper vs PSS comparison: https://our.status.im/whisper-pss-comparison/