name is guaranteed to be constantname 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.
*There might be some goofiness with area51 created sites in this regard, we'll keep you posted when the details shake out.
Update. So
The proper way** to lookup site data is to key off of the current domain (http://stackoverflow.com, for instance, site_url*.
Use one of them basically) and resolve old/cached entries using aliases.
Its probably going to be months from now before any site returns anything in /users/{id}/associatedaliases is not vectorized (as a part of stackauth and not api- whenever WebApps becomes.*.. not WebApps, assuming it doesn't follow the "allever does {id}'s are vectors" rule) and thus you should be able to keep track of that information yourself easily- buts its spec'd.
*There might be**As opposed to synthesizing some goofiness with area51 created sites"key" and trying to hold it constant in this regard, we'll keep you posted when the details shake outface of changing site data. Pro-tip, this is how the SO engine works!