Terahertz (THz) communication has emerged as a key enabler for sixth-generation (6G) networks, offering ultrawide bandwidths to support data-intensive applications such as holographic telepresence and immersive extended reality. Recent advances have enabled both electronics-based and photonics-based THz front-ends, each with distinct advantages and hardware limitations. While electronics-based solutions leverage mature semiconductor platforms, they suffer from amplified oscillator phase noise, frequency offsets, and nonlinearities introduced by multiplier and amplifier chains. Photonics-based systems, in turn, enable highly tunable and spectrally pure carriers but are subject to laser intensity noise, amplified spontaneous emission, shot noise in photomixers, and thermal noise in RF mixers. This article provides a comprehensive review of experimental demonstrations in electronics-, photonics-, and hybrid-based THz links, highlighting their hardware architectures, performance metrics, and implementation trade-offs. We then survey theoretical modeling efforts, emphasizing how hardware impairments affect system reliability and identifying limitations in existing studies. Building on this, we develop comprehensive signal models for both approaches, derive analytical expressions for signal-to-noise ratio (SNR), and evaluate bit error rate (BER) performance under realistic system parameters. Comparative results demonstrate how distinct impairment mechanisms shape the overall link performance of electronics- versus photonics-based THz systems. The insights offered aim to guide the design of robust transceiver architectures and accelerate the integration of THz technologies into future 6G deployments.