VHF (VERY HIGH FREQUENCY MICS) provide extremely clear and good transmission in the right circumstances. are generally with no selectable channels but some do have selectable channels. If they dont have selectable at an event another wireless microphone can interfere with yours but using them when no others are being used is fine. Also in built up areas depending on frequencies sometimes wireless transmitters from security companies can interfere in a 500m range. though rarely. Best used in safe settings and speaking rather than live vocal singing .
UHF (ULTRA HIGH FREQUENCY MICS) are always encrytped channels so cannot be interfered with.They may also have various channels which are selectable - some more than others, so are safer at events when other microphones may also be being used. Also they generally have better quality for more professional use like vocal singing