I need something and have to go by the wire diameter. About half the sites give it in AWG, and the others in metric, so I looked up the conversion. A nice summary here http://www.technick.net/public/code/..._awg_to_metric.
Is it ever simple compared to the AWG values. It's just the diameter in mm, and a mm is a nice size to start with for wires. You can make a wire any size you want, and don't have to type 26 and a half gauge, or something like that to describe it accurately.
It's so simple that when you are given a value you have a good idea of just how thick it is. No tables with the gauge and the diameter needed. I appreciate simple, and at least for this metric has my vote.
Some of the sites give the metric sizes as the cross sectional area in square mms. Not quite as simple, but not bad.