Dear asfeiza, which way of modelling reinforcement is the most effective one depends not only on the profile and amount of the reinforcement and the concrete member around it, but also on the type of loading, etc. To give a general recommendation, use discrete bars. If there would be multiple bars of the same direction in a single element (e.g., because of large finite elements), or if there would be a lot of bars and where detailed modelling is not needed, it makes more sense to model them as smeared reinforcement.

For a typical beam under bending load or a plate (especially when modelled with shell elements), it frequently makes sense to model the longitudal bars as discrete reinforcement, and the stirrups as smeared reinforcement.