The powered descent guidance problem requires considering the six-Dof dynamics model to ensure the guidance performance. The complexity can be reduced by simplifying the dynamics model, such as neglecting rotational dynamics, but this may decrease the accuracy of the solution. This paper compares three design dynamics models for powered descent guidance problem. The numerical experiments show that, under the minimum propellant performance index, neglecting rotational dynamics leads to a considerable decrease in solution accuracy. This paper suggests that by adding a penalty to angular rates in the performance index and using trimmed thrust vector angles, the solution accuracy of the simplified model can be significantly improved with only a marginal propellant loss. This has implications for engineering applications.