It depends.
If you are indoors or somewhere with a lot of obstructions, use UHF.
These would be places like school buildings, hotels, hospitals, construction sites, retail, warehouses, or a college campus. These areas have lots of buildings, walls, and other obstructions where UHF is better equipped to handle.
If you are in areas free of obstruction you should use VHF. These would be road construction, farming, agriculture, ranch work, etc.