I actually tend to draw my characters, or try to, at least. Sometimes I have the image in my head, but can't get it onto my paper. When that happens, I use a description.
But I use a cartoon like style, and when drawing cartoon characters, the big thing is to let the audience know what their personality is, just by their design. This sort of applies to my writing, too. I want people to figure out what my characters are like, just by the description.
Then again, a lot of times I like to avert expectations, so sometimes I break my own rule.
...I trailed off topic a little, didn't I? I'm sorry.