However, if you compare AC's Executive First with almost anyone elses' first class product, you will invariably hear that it is an unfair comparison, as AC's "first" class is actually only business class.

Nevertheless, AC's "premium" service is quite variable, primarily dependent upon the plane, which is in turn (partly) dependent upon the route. The service you get on an A330/340 on YVR-YYZ will be vastly better than the service you get on a DC9 on YVR-EWR.

Can't speak to UA, but comparing AA to AC I'd say that you get a more comfortable seat on AC, but better food on AA. Service on AA seems to be consistently good, while service on AC ranges from scary to excellent, depending on what number you rolled when you got out of bed.