There are a lot of factors determining the value of a domain. One of the most common is the count of alphanumerics. The shorter it is, the more valuable. The number of words also comes into play unless a group of words is something iconic or it is a popular expression. As for set of numbers, those combination that are easy to remember (i.e. 1234, 000, 888), distinguishable (i.e. 911, 143) might get more preference. Some CNS offer special characters and unicode such as emojis which are more valuable than alphanumeric combinations. Even part of speech like nouns, pronouns, adjectives, verbs, and etcetera are being highly considered. be the TLD or Namespaces from different blockchain.