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

Explication

SSB puts all the transmitted power into one narrow sideband, roughly 3 kHz wide instead of the 10 to 15 kHz an FM signal occupies, so the receiver's noise bandwidth is far smaller and the signal stays readable at levels where FM has already dropped below its noise threshold. This is why weak signal VHF and UHF work is done on SSB, not FM.