This paper compares different models that can be used to analyze the vibrations of an unbalanced rotor with horizontal axis over a flexible tower. Model results are compared with experimental results. The modeled system is equivalent to a wind turbine with perfectly rigid blades. The selected models are the linear elastic model that is obtained using the linear theory of vibrations and two multibody models. The first multibody model uses Component Mode Synthesis for the description of the tower flexibility while the second multibody model used a lumped properties approach. Experimental results validate with reasonable agreement the resonance speeds of an unbalanced rotor. Furthermore, the models, while low degrees of freedom, give valuable insight of inertial loads on drivetrain components based on tower top dynamic motion. The work presented in this paper showed the use of 3 low-degrees of freedom models to predict resonance and tower top displacements. All simulation models did exhibit slightly higher resonance frequencies than the experimental results. The results showed that the tower top motion for the rectangular tower resembles a figure eight type motion, while the square tower top shows an elliptical motion.