Which is better QPSK or QAM?

In AM, the amplitude of a high-frequency carrier signal is varied in proportion to the instantaneous amplitude of the modulating message signal. Frequency Modulation (FM) is the most popular analog modulation technique used in mobile communications systems.

For speeds of 400 Gbps and beyond, however, 16-QAM is preferable because of its easier implementation and better optical signal-to-noise-ratio performance due to the larger distance between the constellation points. FIGURE 9. Constellation diagrams for APSK schemes and corresponding QAM formats.

yes , FSK is better than ASK in the cases that the carrier has a constant amplitude and hence are used in the communication systems wher security reasons are considered …. but it cannot be said that it fades less as over long distance communication its SNR decreases and hence quality of signals …

The primitive difference between the QAM and QPSK is that the spectral width of QAM is narrower than the QPSK. Furthermore, the BER (Bit Error Rate) of the QAM is higher than the QPSK. … Comparison Chart. Basis for comparisonQAMQPSKPerformanceAverageBetterBit error rateHighLowDifference between QAM and QPSK (with Comparison Chart) techdifferences.com › difference-between-qam-and-qpsk

Higher order QAM modulation schemes are vulnerable to error. Therefore, error correction coding ensures higher chances of signal survivability in AWGN and multipath Rayleigh Channel and thus enhances the performance of the system.

Amplitude modulation methods like ASK/OOK and QAM are far more susceptible to noise so they have a higher BER for a given modulation. Phase and frequency modulation (BPSK, FSK, etc.) fare better in a noisy environment so they require less signal power for a given noise level (Fig.14 Tem 2021