This has been brought up a couple times before, and in my experience, there are basically three answers:

Screw it, Use Eloquent

Good: Eloquent, in all it's glory
Bad: Switching data sources is a big pain in the ass, especially if you liberally use the query builder for relationships

Create an Entity Interface, Have Your Eloquent Model Implement It

Good: Switching implementations requires much less effort, and the only wildcard is wrapping your eloquent-specific methods and including them in the interface and making sure you document the entity's properties
Bad: Relies on developer discipline to not leak Eloquent's implementation details into your entity, you give up on a lot of Eloquent's conveniences

Create a Separate User entity, Map Your Eloquent Model to it and Back

Good: You don't need to worry at all about switching repositories breaking your existing code
Bad: You have to implement a mapping layer to translate eloquent models to your entity classes, and will need to do so again if you implement another repository.