TIG can be all over. From a 9 with low amperage on very thin steel, to 13 or more for high power on polished aluminum. A lot depends on the person, too. Whatever you need to see the puddle is what it takes. The distance can change things a little, too. Age has forced me to use a cheater lens now, to be as close as I like to.
That is another real advantage to an auto dark, most you can dial in just what shade you want.
But they all seem to have the same look to the shade. I really liked some of the gold foil shade lenses and the color of an aluminum puddle through them. I have not seen an auto dark that looks like that. If anyone knows of one, I would love to hear about it.