A comparative analysis of the results of determination of the work of critical cluster formation in nucleation theory for three different methods of evaluation-Gibbs' method (employing the capillarity approximation), the van der Waals-Calm and Hilliard method, and a newly developed modified Gibbs approach-is given. As a particular application, the processes of condensation and boiling in one-component fluids are analyzed. As a model system for comparison, van der Waals fluids are chosen. In addition to the work of critical cluster formation, the bulk properties of the critical clusters (drops or bubbles), their characteristic sizes, and the values of the surface tension are determined in dependence on the initial supersaturation in the system or, equivalently, on the size of the critical clusters. It is shown that latter two mentioned methods of determination of the work of critical cluster formation (the van der Waals-Cahn & Hilliard and the modified Gibbs approach) lead-at least for the model system considered-to qualitatively and partly quantitatively equivalent results. Nevertheless, differences remain which may lead to quantitative deviations when applied to the determination of the steady-state nucleation rates and further basic characteristics of nucleation-growth processes. The possible origin of such deviations is discussed, and some further directions of analysis are anticipated.