More seriously they are aimed at different markets. Seaweedfs seems like a great project for simple clusters, and I've used it to store 600Gb without problems. But do bear in mind the bug tracker has several issues relating to backups failing, corruption, and similar. You'll need to check your backup-system and assess how serious they might be.

Minio started out as "just" an S3-compatible storage system, I've not used it much but certainly I found that I could interface to it with the existing Amazon S3 clients very easily. I've not used that in a distributed setup, just on a single node.

Both seem well-documented. Both seem "active".

Pick the one that makes most sense to your use-case ("distributed storage" vs "distributed storage with known-API") and report your bugs as you find them.