Which type of voice mode is often used for long-distance (weak signal) contacts on the VHF and UHF bands?

Single Sideband (SSB) is the preferred voice mode for weak-signal, long-distance communications on VHF and UHF bands. SSB is highly efficient because it eliminates the continuous carrier wave and one sideband, focusing all of the transmitter's power into a narrow 3 kHz slice of spectrum. In contrast, FM voice is excellent for local, static-free communications but performs poorly for weak signals. FM spreads power over a wider bandwidth and suffers from a rapid drop-off in intelligibility when the signal gets weak, whereas SSB signals can often still be understood even when buried in background noise.