It really depends on what I am drinking. If I am having what I call "proper" English Tea, that is, tea that has been imported from the UK or that I'm drinking in the UK, I want my cup to be bone china. It NEEDS to be Bone china, it effects the taste otherwise.
However, if I'm just drinking coffee or hot chocolate, soup - whatever, I like a big, large, open-mouthed cup, something big enough I can drop my phone into (which I have done). I like being able to wrap both my hands around it and have all of my palms and finger tips on it to warm up.
My favorite one at home is one I got from a pottery painting place, and I painted the Universe on it...not the best work, but definitely mine. Though my roommate seems to have decided it's her favorite one as well, and keep a good hold on it.