The electrochemical sensing properties of graphene-based and carbon nanotube (CNT)-based electrodes towards ascorbic acid, dopamine, uric acid, and glucose are systematically compared. Nano-sized Pd catalyst particles are uniformly dispersed on both carbon supports using a supercritical fluid deposition technique to increase the sensing performance. The CNT/Pd electrode shows higher detection current than that of the graphene/Pd electrode, which is attributed to the three-dimensional architecture interwoven by the CNTs that creates a larger number of reaction sites. With the incorporation of ionic liquid (IL), the detection sensitivity of the IL/graphene/Pd electrode significantly increases, becoming noticeably higher than that of the IL/CNT/Pd counterpart. The synergistic interactions between graphene and IL that lead to the superior sensing performance are demonstrated and discussed.