Modern front-end frameworks face escalating reactivity management challenges, including performance degradation from complex observable chains and unpredictable re-renders. This paper introduces Signal-First Architecture--a novel paradigm where granular, dependency-tracked signals are the atomic unit of reactivity. Unlike traditional RxJS or NgRx patterns, Signal-First enforces reactive flows from explicit signal declarations, with derived values via computed() and side effects scoped to effect(). This model ensures deterministic behavior by eliminating implicit subscriptions and optimizing reactive graph evaluation. We present a comparative analysis of three Angular reactivity models: RxJS service-based, NgRx global stores, and pure Signal-First implementations. Through controlled benchmarking, including Chrome DevTools performance tracing, memory heap snapshots, and Lighthouse audits, this study quantifies Signal-First advantages.