The option to select between structural and behavioral models is mainly to improve simulation run times. Almost all cores contain a structural model, but not all have behavioral.
Behavioral would typically provide faster simulation run times. This is due to the fact that structural models are built out of the lowest level primitives and all need to be compiled when simulating.
Neither of these models contain timing delay information. Timing delays are included post implementation. Both should produce the same simulation output. Any exception is noted in the core documentation.