For me it's been trial & error.
I haven't noticed any difference in durability from one diameter of serving to the other.
If the nocks are too tight, use thinner serving. If they are too loose, use thicker.
There are so many different recipes for strings that it's difficult to give advice about which size serving will work the best over the internet.
I just serve up a inch or two. If it's good, I keep going. If it's too tight or too loose, I make a change.
Guys who make strings professionally, will have a much better feel for which serving to use.
Nock fit is one of the details of accurate shooting. It's not a big item, but certainly one that needs attention.