Bob vs Ent
Source of truth
Ent is code-first. The schema is defined in code and it then generates the entities using Ent-specific techniques. If you use a different tool for migration, you then have to manually ensure that your Ent schema is in sync with your database.
Bob is database-first. You generate your database using the first class tools for your DB (SQL, pgAdmin, migration pacakges). And then generate your models from your database.
Ent provides predicates to build queries. This covers common usecases and allows for easy graph traversal.
Bob has a more powerful query builder. Across all supported dialects, Bob allows you to build pretty much any Select, Update, Insert or Delete query supported by the dialect.
Ent expects to handle your migrations. It includes automatic migrations for development/testing and versioned migrations powered by Atlas
Bob does not deal with migrations at all. You can use any tool of your choice for migrations (golang-migrate, flyway, atlas, e.t.c) and then regenerate your models whenever the database state is updated.
Ent currently has a more mature ecosystem. For example it includes plugins to integrate with gqlgen and gRPC.
Bob is only focused on the data layer. Although it is possible to hook into the generation process to integrate with GraphQL or gRPC, it is not done at this time.
Ent needs to be adopted fully. It is not possible to use only a part of its features.
Bob can be used incrementally. For example, it is possible to use only the query builder without needing to fully adopt Bob.