I suppose a monocular might be useful in a few specific situations, where size and weight is critical. However, for the majority of situations you are much better off with a good binocular.

In optics, you almost invariably "get what you pay for". I've found a good compromise between decent optical quality, robust construction, and a price I can afford is the Steiner Military/Marine 8/30 binoculars. I've carried a pair for years through my Alaskan adventures, and really like them. Good optics, rubber armor, waterproof, large exit pupil, roll down eyecups for use with glasses, and reasonably light weight.