Which type of voice mode is often used for long-distance (weak signal) contacts on the VHF and UHF bands?
Why SSB puts all transmitter power into a single sideband roughly 2 to 3 kHz wide, with no carrier and no redundant second sideband wasting energy. That concentrated power plus a narrow receiver bandwidth (less noise admitted) gives SSB a big weak-signal advantage, which is why VHF/UHF DX, meteor scatter and EME operators work the SSB portions near the low end of each band.
Watch out FM is the other tempting answer because it dominates VHF, but FM spreads power over 10 to 15 kHz and has a capture/quieting threshold: below a certain signal level it turns to noise rather than degrading gracefully, so it is for local repeater and packet work, not DX.
Narrow beats wide when signals are weak: SSB for DX, FM for local repeaters.