The instrument arguments on this shelf all come down to the same three variables: how much light it gathers, how much it magnifies, and how much friction stands between you and using it. This page compares the four instrument types on those terms.
Binoculars against a telescope
Binoculars win on friction, field of view and comfort, and they use both eyes, which genuinely helps on faint objects. A telescope wins on aperture and magnification, which is everything for planets and faint detail. Most observers own both, and the binoculars get used more often.
A spotting scope against both
A spotting scope is a daylight telescope with an upright image, a zoom eyepiece and a tripod. It beats binoculars for reading detail at distance in daylight and loses to them on finding things and on comfort. Against an astronomical telescope it loses at night on aperture and wins in the day on convenience and image orientation.
Monocular against binocular
A monocular is half a binocular: half the weight, half the bulk, roughly half the price, and noticeably less comfortable because one eye works while the other does not know what to do. It is a pocket instrument for occasional use rather than a serious observing tool, and for sustained viewing a binocular is worth the extra bulk.
Questions people ask about binoculars
Are binoculars or a telescope better for beginners?
Binoculars to start: no setup, a wide field that makes finding things easy, and a view of large faint objects that a telescope cannot frame. A telescope when you want the planets and fainter detail.
What is the difference between a telescope and a spotting scope?
A spotting scope gives an upright image, zooms, and is built for daylight; an astronomical telescope has more aperture, often an inverted image, and is built for the night.
Is a monocular as good as a binocular?
Optically it can be, but using one eye is less comfortable and shows slightly less on faint objects. It wins on size and price alone.