Gelatin methacryloyl (GelMA) hydrogels are widely used in biomedical engineering due to their tunable mechanics, biocompatibility, and applications in tissue engineering and drug delivery. Photopolymerization using different photoinitiators—Eosin Y (EY), Lithium Phenyl-2,4,6-trimethylbenzoylphosphinate (LAP), and Ruthenium (II) trisbipyridyl chloride (Ru)—allows precise control over hydrogel properties, but the effects of varying photoinitiator concentrations remain unclear. This study systematically examines how EY (0.005–0.1 mM), LAP (0.01–0.5 wt.%), and Ru (0.02–0.5 mM) influence the viscoelasticity, swelling, biodegradation, and cytocompatibility of 5 and 10 wt.% GelMA hydrogels. Results show distinct trade-offs: LAP and Ru promote rapid gelation, suitable for bioprinting and injectable systems, but exhibit lower stiffness and faster degradation. Conversely, EY enhances stiffness and long-term stability, though with a more complex crosslinking mechanism. The choice of photoinitiation wavelength also impacts cytocompatibility, as LAP requires UV light, while EY and Ru use visible light, improving biocompatibility. The findings of this study provide key insights for selecting photoinitiators based on processing simplicity, mechanical performance, and biocompatibility, advancing GelMA applications in tissue engineering and regenerative medicine.