This paper compares various thermo-fluid modeling methods and their impact on the computational time and accuracy of engine performance calculations. The use of accurate fluid models is essential because the thermodynamic calculation of every engine component relies on them. Various fluid models have been discussed in the literature, mostly for air and the combustion of hydrocarbons. This work proposes adapted polynomial-based fluid models that combine the advantages of fast and simplified models, such as the Walsh and Fletcher polynomials, and fuel-flexible, slow and accurate models, such as NASA's Chemical Equilibrium and Applications, by taking into account dissociation and pressure effects. A comprehensive analysis of the fluid models is performed to investigate their impact from engine station level up to flight mission comparison level. It is concluded that the consideration of dissociation and pressure effects is of high importance for in-depth analysis up to the mission level. However, for comparison of novel technologies at flight mission level, all fluid models show deviations below the uncertainties of emission or climate models and are therefore suitable. Fluid model recommendations are given for each level in this paper. Depending on the application, fine-grid fluid tables and the developed adapted methods are most appropriate.