I prefer that we use the channel ID globally. This came from my experience working with YouTube's API for the List of Untergangers updater script.
The IDs for channels are permanent for each channel, and is the principal way of accessing the API. In the event that a channel later closes, or become suspended/terminated, we can detect that by querying the API with the channel ID (i.e. the details are gone but the ID persists, and the API throws an error).
Unfortunately, there's quite a few channels that we'll never know the IDs of on the List of Untergangers, only their old usernames, either because of typo or because the channel has closed. The API couldn't associate usernames of dead channels to their IDs.