Thanks for bringing up this discussion!
In my opinion, Hyperledger Sawtooth supports both permissioned and permissionless blockchain implementation whereas Hyperledger Fabric support only permissioned blockchain implementation.
Hyperledger Fabric is a distributed ledger platform that delivers resiliency, scalability, flexibility and confidentiality. Hyperledger Fabric enrolls members via a trusted membership service provider. Hyperledger Sawtooth can be configured to operate as a public network.
Here is the article I came across which explains every detail about hyperledger. Click here to learn more.
Hyperledger Sawtooth Architecture
Hyperledger Fabric Architecture
Hope you enjoy this read. Always open for discussion.