Always,absolutely ALWAYS, my first name!!! I am divorces so I am not a Mrs any more,and I am also not a Miss!! I hate the use of Ms as it is neither this nor that to me!!! Even when I was married I still liked being introduced using my first name.It is who I am!!!
I find being addressed by my first name very personal, and intrusive and presumptuous if it is being done by a stranger.
I really liked being addressed as "Madame" (say it with a French accent!) when I lived in Belgium and was sorry to move to Germany where I became "Frau" which just sounds frumpy to me. Back home in England now, practically no-one calls me Mrs, so I have to squirm or interrupt when they address me by my name.