Asexual reproduction is much faster and less energy and time consuming than sexual reproduction. It doesn't offer the important advantage of genetic diversity like sexual reproduction does, though.
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It is better in some cases. For example, if an animal is an interspecific hybrid, then it may not be able to reproduce sexually, since meiosis may fail because the chromosomes do not line up correctly. It is better if an animal colonizes an island, and there are no members of the opposite sex around. Overall though, and over the long run, sexual reproduction is better because it promotes genetic diversity within the gene pool.