the perfect mug, for me, is as follows:
- straight sides and not fluted (i.e. the same diameter at the top as at the bottom)
- pottery, not china.
- the depth of the mug must exceed the diameter of the mug
- ideally, glazed white on the inside (easier to judge the right colour of tea that way)
- no funny business with the handle
- decoration: not fussed - i'm quite the fan of mugs that relate to some kind of public-funded information campaign (my current mug reads "SAY NO! closing the door on bogus callers")