rich, for the synthetics I stock both 16 and 17 gauge. For the poly strings, I typically stock 17, although I will at times carry sets of the 16. For instance, I carry Super Smash Honey in 16 because that is what my wife plays with. I'll stock some BHT 16 because most people prefer or request that gauge.
If I had a choice to only stock one gauge, it would be the 17. Typically it is much livelier, and not as abrasive.
Roger Federer Pro Staff 97 Play test video