Bone china all the time. Can't be doing with thick china. Our local garden centre restaurant serves coffee in mugs as thick and heavy as terracotta plant pots. Yuk!
I'm with Tanith on this one. Reminds me of (some of?) the reasoning behind milk in first, or milk in last.
It seems that years ago when the upper classes used bone china and the lower orders used pottery mugs for their tea, the lower orders put milk in first in order to avoid the mugs cracking from the boiling water; the upper classes had no such risk with bone china - which allowed them to put the tea in first and then add milk or lemon according to taste.
My mum was the one for her china cups/ tea -sets. She had a beautiful Spode teacup that was her favourite for her tea but my ex-SiL beat me to it after mum died---as did the Crown Derby tea -set vanish Ah well I've got the old Colclough, which I don't use.
It's a mug for my coffee and a china mug for my morning tea which I have to soak in bleach now and again because of the tannin stain on account of me liking builders tea.