Ken,
I understand the gauges you are currently considering. They'll be a good market for the 12 and 20 and likely the 16 will get some decent interest. But, I just haven't warmed up to the 16, especially in a modern load capable gun comparison. I'm of the opinion that a 20 and a 12 bridge this gap nicely with modern loads. A slightly heavy 20g load or a light 12g load pretty much does it for me.