`name` is guaranteed to be constant.  So is `site_url`*.

Use one of them.

`/users/{id}/associated` is not vectorized (as a part of stackauth and not api.* it doesn't follow the "all {id}'s are vectors" rule) and thus you should be able to keep track of that information yourself easily.

<sub>*There *might* be some goofiness with area51 created sites in this regard, we'll keep you posted when the details shake out.</sub>