Agreed. 16mm is wide enough to be different but still tight enough to work as an environmental portrait lens. 23mm is my favourite overall, and it's what I'd choose if I had to pick one lens. And 56mm is tight enough for headshots but still wide enough to be versatile.
Right now I have the 18, 23, and 35. Sort of the poor man's version of that setup. I got the 18 over the 14 for the size and speed, but the 16 would negate either of those for me.
