The approach of reducing the number of opamps in the loop filter of a delta-sigma modulator (DSM) using single-opamp resonators (SORs) has been introduced in many state-of-the-art designs. The intention of this approach is to increase the power efficiency and decrease the circuit complexity of the design. Various SOR architectures with different RC combinations have been introduced in different designs. Even though some of those SOR based DSMs showed very good power efficiency, it remains an open question if the approach generally yields improved power efficiency or require a single opamp with much higher requirements compared to the conventional multi-opamp approach. This work compares the noise behavior of different SOR architectures introduced in the literature on analysis as well as simulation level. This is an important aspect in the design process, where the noise requirements commonly determines the required power consumption. It is shown that the noise behaviour of SOR significantly differs.