I am a characterization fan, and I prefer descriptions right at the beginning so I don't form an image that is contradicted later.

One of the things that bugged me about the last Wild Cards book I read is that they didn't bother with much physical description in the book because the book has a webpage with comic book style art, and that defined how the characters looked. If not for that, I wouldn't really have had a clear picture of anybody other than one. And it would've bugged me worse.