US or USA it's the same place, ain't it? US of A is more "corny" than "in your face" but I use it once in a while.
I kinda like the way Merriwether Louis referred to us as the "U. States". If you DO use US of A then you can also use "Amurrican".
I once teased a former Sinn Fein representative from North Belfast by asking him if he was "from the British Isles". My daughter (a friend of his) had to intervene. She explained to him that I had an odd sense of humour.