Rapid urbanisation demands walling materials that are simultaneously energy-efficient, low-carbon and affordable. This paper presents a multi-criteria comparison of Autoclaved Aerated Concrete (AAC) blocks with conventional solid and hollow concrete blocks across physical, mechanical, thermal, acoustic, structural, economic and environmental indicators, benchmarked against IS 2185 (Parts 1 and 3), IS 6041 and IS 6441. Compressive strength, thermal conductivity and capillary sorptivity were determined on fifteen AAC and fifteen concrete block specimens at NABL-accredited laboratories, while the remaining parameters were compiled from Indian Standard limits, manufacturer data and published literature. Although concrete blocks develop higher compressive strength (5.0–15.0 N/mm² against 3.0–4.5 N/mm² for AAC), AAC masonry reduces wall self-weight by about 70 per cent, jointing mortar consumption by 75 per cent and thermal transmittance by 76 per cent (0.78 against 3.25 W/m²K). For a ten-storey commercial building modelled in Seismic Zone III, AAC infill lowered structural steel by 8.5 per cent and concrete volume by 6.8 per cent, giving a 10.2 per cent reduction in total structural cost, while Energy Plus simulation indicated an 18.3 per cent annual cooling energy saving. Embodied carbon is 54 per cent lower per square metre of wall. An engineering decision matrix is proposed to guide material selection

Autoclaved aerated concrete; Concrete masonry units; Thermal transmittance; Embodied carbon; Life-cycle cost.