I don't know when mugs became the drinking cup of choice for hot drinks, but I much prefer a cup - and a fluted one at that.
It's true that a thick mug retains heat better than a porcelain cup, so I can understand those who come downstairs in the morning to make a mug of tea (first warming the mug) before taking it back to drink in bed, but even then a fluted mug is better than a straight-sided one. The reason is that it is difficult to sip out of a straight-sided cup and so one's first few sips of the hot liquid are liable to result in the tea escaping down the sides of one's mouth. This is because when sipping, the point at which the mouth meets the lip of a straight-sided the cup is narrow and does not allow a seal to be made with the rim of the cup. On the other hand, the architecture of a fluted cup or mug allows the mouth to create a wide seal with the rim, making sipping the hot drink comparatively drip-free.
This reminds me somewhat of this lovely poem
