The transition to a low-carbon energy system and the emergence of a hydrogen economy have increased the need for large-scale, reliable subsurface storage of carbon dioxide, hydrogen, and natural gas. Selecting suitable storage sites requires balancing geological, technical, environmental, economic, and social criteria, while accounting for the distinct physical and chemical behaviors of each gas and the intended service. This paper adopts a unified, gas-aware framework to synthesize site-selection criteria and decision-support methods for subsurface gas storage across the principal geological options: deep saline aquifers, depleted hydrocarbon reservoirs, and salt caverns. The study examines decision-making approaches ranging from conventional multi-criteria decision-making and fuzzy extensions to Geographic Information System-based spatial analysis, reservoir simulation, and emerging machine-learning techniques for large-scale screening and uncertainty quantification and mitigation. Drawing on global case studies, it identifies methodological limitations, gas-specific knowledge gaps, and data challenges that constrain confident site selection, particularly for hydrogen storage in deep saline aquifers and depleted reservoirs, including reactivity and microbial consumption risks, purity and mixing constraints, and cushion-gas economics. Future directions emphasize the need for integrated, explainable, and adaptive decision frameworks tailored to gas-specific behaviors and storage contexts; expanded large-scale H₂ demonstrations in saline aquifers and depleted reservoirs; tighter coupling of monitoring, modeling, and decision tools throughout the project lifecycle; and regulatory frameworks that clarify long-term liability and strengthen public engagement and trust. Collectively, these insights provide a structured basis for developing robust and transparent decision pathways for strategic subsurface storage in support of energy-transition objectives.