I don't like Arthur. My associations with it are a combination of King Arthur, old men, and Arthur the Aardvark. It sounds alternately a bit stodgy and a bit silly, and I hate how people sometimes pronounce it like "author." I guess I'd rate it about a 5. It doesn't go any lower because it's a classic name with a nice history and all, but it just doesn't appeal to me.
I could see Arthur with siblings with primarily very British names... Alasdair, Barnaby, Walter, Victor; Imogen, Charlotte, Georgia, Beatrice.