All other things being equal, give preference to words with fewer syllables and words that are easy to pronounce. Short is good, but don't use difficult to remember acronyms, such as qmxf. DO register a long domain name containing a list of relevant words for your web site to achieve a higher ranking in some search engines. Several of the major search engines rank web sites much higher if the search terms are contained in the domain name. You can use up to 63 characters to create a long domain name with keywords and automatically redirect visitors to the real web site.
Some registrars offer the redirect service as standard in their price.
DO use the appropriate pluralization. DO use words that can be visualized. Vision is the strongest of human senses. Even better, use words that involve several of the 5 senses. DO plan for the future.