Leaky mode resonance (LeMR) and lossy mode resonance (LoMR) refer to two different surface waves but are easily confused. Herein, we comprehensively investigated the excitation mechanism and sensing performance of both LeMR and LoMR with the same prism-film-surrounding platform based on the rigorous transfer matrix method. Both non-absorbing film waveguides, absorbing film waveguides, and gold-cladding film waveguides were analyzed. Our findings reveal that degenerate LeMR occurs across all configurations while polarization-dependent LoMR emerges only in the latter two cases, with their appearance determined by the corresponding critical angle of the incident wave. This spectral difference leads to different sensing performances for surrounding refractive index (RI) detection. In particular, the LeMR remains sensitive to the RI changing in a wide range, achieving the highest sensitivity as the prism-film-surrounding becomes optically symmetric. In contrast, the LoMR operates exclusively for the surrounding RI lower than that of the prism. The results also suggest that the LeMR exhibits flexibility in film material selection while the LoMR offers the advantage of a narrower bandwidth.