It's a big question, and one not easily answered.Binoculars are more popular, and there's a much greater range from which to choose. They're generally considered to be more comfortable if you're using them for long periods. You're using both eyes, so your depth perception is better. You also have a wider FOV.Monoculars are easier to make, so you either get the same magnification at a lower price than binoculars, or you get considerably more magnification if you spend about the same amount of money. Monoculars are much more compact. Small night vision monoculars are favored by armed forces, though many of the less-expensive models are quite large. Some hunters prefer monoculars for spotting.