It's hard to say which number would have the most value as they all have different meanings. For example, 123 has a common phrase "easy as 123", 247 is a representation of 24 hours a day 7 days a week, 360 is relatable to 360 degrees or a circle, and 365 is the numbers of days in a year. These are all completely different associations that could be applied to the domain prefix. Without knowing the first part of the domain a value can't really be determined. The obvious answer though is whichever number is the most applicable to the prefix. If none of they are I would move on and find some other domains to register.