Frame it as a trade-off: "Eloquent is faster to develop with for simple CRUD. Doctrine is better when domain logic is complex and I need entities that are independent of the database."
Active Record (Eloquent): model classes map directly to tables, simpler for CRUD, but business logic can leak into models. Data Mapper (Doctrine): entities are plain objects, the mapper handles persistence separately, better separation of concerns but more setup. Strong candidates discuss testability, complex domain logic, and when the overhead of Data Mapper is justified.
Senior question testing ORM understanding beyond basic usage. Candidates who cannot articulate trade-offs likely have not worked on complex enough projects. Look for experience with at least one pattern in depth.