Short Answer
Choose Glean if the core job is enterprise search: finding answers across documents, chat, tickets, drives, wikis, CRM, engineering tools, and other workplace systems while preserving source permissions.
Choose Guru if the core job is governed knowledge operations: keeping answers accurate, cited, verified, permission-aware, auditable, and available inside the tools where employees already work.
If you are still building the category shortlist, start with best AI enterprise search tools and best AI knowledge base tools.