I really try to avoid Sharpie. Years ago I would use it to get autographs on items, but the lines of the Sharpie are often way too fat, and tend to blur the beauty of the signature.
Fortunately, most pre-war HOF signatures are not available in Sharpie. I'll take a crisp and bold fountain pen every time. Can you imagine what this would look like if Speaker signed it in Sharpie? Not good!