The article is dedicated to the comparative evaluation of rigid, hinged, and semi-rigid beam-to-column connections in steel frame systems, depending on building height and span. The relevance of the study is determined by the increasing demand for optimized structural solutions that ensure stability, seismic resistance,e and economic efficiency in multi-storey steel construction. Scientific novelty lies in the system-level comparison of connection typologies through stiffness normalization and deformation sensitivity thresholds rather than isolated strength assessment. The work describes the influence of fixity-factor variation on column resistance and drift amplification and studies the transition of governing structural mechanisms from strength-dominated to deformation-controlled behavior. Special attention is paid to stiffness deviation tolerance and its impact on multi-storey sway frames. The aim of the study is to establish quantitative stiffness and deformation thresholds that define rational application domains for rigid, semi-rigid, and hinged connections in steel frame systems. Comparative analysis, source synthesis, and analytical evaluation methods are used to solve this problem. The conclusion describes structural thresholds that redefine connection selection as a system-level optimization task. The article will be useful for structural engineers, designers, and researchers in steel construction.