Resonant label-free biosensors using silicon-on-insulator substrates represent a cutting-edge domain in optical sensing. These devices leverage the high refractive index contrast of silicon-on-insulator materials to create highly sensitive, compact sensors. They are crucial for real-time, precise biomolecular detection in healthcare diagnostics, environmental monitoring, and drug discovery, marking a significant stride in microphotonic technology and its practical applications. Different ring-based resonant configurations have been explored in this context, but a definitive comparative assessment of them was previously lacking in the literature. In our work, we experimentally compare four different ring configurations in terms of figure-of-merit (FoM), showing that the slotted ring performs better than competitive approaches. A silicon photonic chip including tens of ring resonators (RRs) was fabricated and optically characterized considering air and aqueous solutions as cladding. The best sensitivity achieved was 64 nm/RIU for the slotted ring configuration. The ring displayed a Q-factor in the order of <inline-formula> <tex-math notation="LaTeX">2.57\times 10^{{4}} </tex-math></inline-formula>, and the best estimated resolution was in the order of <inline-formula> <tex-math notation="LaTeX">{10}^{-{4}}~\text {RIU} </tex-math></inline-formula> in water. The measured FoM was greater than <inline-formula> <tex-math notation="LaTeX">{200}~\text {RIU}^{-{1}} </tex-math></inline-formula>.