Personally, I'd go with the Glacier. I've never used it, but the substitution charts say US Fuggle, Willamette and Styrian Goldings (both Fuggles cultivars), and Fuggles are appropriate for the style. Hallertau would be my second choice.
Really, any low cohumulone variety would work well, because there should be no noticeable hops flavor or aroma in Mild. Unfortunately, that rules out most of the American varieties; it's been my experience that American varieties still taste like citrus no matter how long you boil them. And in such a delicate beer as Mild, that flavor is objectionable.