Photon-counting detectors (PCDs) can resolve the energy of incident x-ray photons, which allows simultaneous imaging of two contrast materials, such as iodine (I) and gadolinium (Gd), with a single scan. This capability may allow reduction of patient radiation dose for clinical applications that typically require multi-phase acquisitions by injecting different contrast media at different times and scanning only once to differentiate, for example, venous and arterial phases. The material decomposition performance on PCD-CT is dependent on acquisition setup including tube potential and energy thresholds. In this work, we performed a phantom study to evaluate the optimal acquisition settings for dual-contrast imaging using I and Gd on a research PCD-CT system. We further compared our results with a clinical dual-source dual-energy (DSDE) CT. An abdomen-shaped water phantom with I and Gd inserts of different concentrations was scanned using different energy thresholds and tube potentials to identify the optimal setup for I and Gd quantification. Results demonstrated that accurate quantification of I and Gd concentration was possible using the PCD-CT system. A tube potential of 80 kV and an energy threshold close to the K-edge of Gd (50 keV) was found to yield the best performance in terms of measurement root-mean-square-error (RMSE = 4.4 mg/mL for I and RMSE = 3.3 mg/mL for Gd). Further, the performance of PCD-CT with optimized setup was found to outperform DSDE-CT (RMSE = 8.1 mg/mL for I and 5.7 mg/mL for Gd).