Personal preferences:
The smaller the better, as long as it's legible. Cup and Dagger is not the easiest to read, so I've replaced it in several windows. Too often the background skin is such that text disappears in the pattern of it, especially those with light & dark swirls, where whole ranges of color blendinto some part of it or another. I've changed a couple of mine to the plain background for this reason.
Tall & thin is better than a wide box, as they lend themselves to docking as a sidebar more easily and are less obstructive.
Where there is text to be read, as in descriptions, too narrow and the wrapping gets ugly and harder to read, so a layout that allows for description boxes to show a bit more by being wider and less scrolling is perferable than narrow-as-a-news-column and miles of scrolling.
Wherever practical, resizable is generally preferred than fixed if the widgets will scale with the window.
Poll
