Complementary field-effect transistors (CFETs) have emerged as promising candidates for next-generation semiconductor devices. CFETs feature a structure with an nMOS (or pMOS) transistor at the bottom and a transistor of the opposite type at the top. CFETs can be classified into Fin-CFETs or GAA-CFETs based on their channel structure. In this study, we compare and analyze these two devices to determine which structure is more favorable for device scaling and which device exhibits better performance per unit area. For a reliable analysis, the threshold voltage was adjusted to be the same for all devices. Initially, to compare the DC performance, the on-state drive currents in both linear mode and saturation mode operations were extracted and compared from the$I_{\mathrm { DS}}$-versus-$V_{\mathrm { GS}}$input-transfer characteristics. Subsequently, complementary metal-oxide-semiconductor inverters were constructed to compare their AC performance. Six parameters were extracted and compared: high-to-low propagation delay ($t_{pLH}$), falling time ($t_{f}$), low-to-high propagation delay ($t_{pLH}$), rising time ($t_{r}$), overshoot voltage ($V_{ov}$), and undershoot voltage ($V_{und}$). Based on the results, we suggest which CFET structure is more suitable for device scaling.