T. Rex is still one of the few adults in the room in this administration.  I know that meme has been beaten to death, but that makes it no less true.  He seems to be among the few who act with any sort of dignity and understands the gravity of his post.  
Nikki Hailey on the other hand seems like a personal striver who will do pretty much as trump tells her so long as it also serves her personal interest.  In other words a typical trump administration member.  I hope I'm wrong about that.