As someone who currently lives in San Francisco and enjoyed Ample Hills while still in NY, I can say this definitively: Ample Hills is much, much better.Don't forget about Ghirardelli. Sundaes are at least $9.45, with shakes starting at $6.50 for a small. Ample Hills seems comparable, if not a higher-quality product.
Ghirardelli is basically a 'Walmarted' brand out here, a mass machine that churns tourists in and out who pay stupidly high prices (which are always 'discounted', funnily enough) for chocolate items when the exact same chocolates are available in generic pharmacies and grocery stores (at lower prices) across the city/state/country.
If you came to San Francisco, Ghirardelli wouldn't be the first place I'd recommend to buy chocolate. It wouldn't be in the first 5 places for ice cream, or 10 places for dessert. In comparison, Ample Hills might be a top 3 ice cream spot in NYC, and the visitors of WDW should be thanking their lucky stars that Iger got a brand like this to open a storefront in a beautiful Boardwalk location and only charge a few more cents than comparable servings of icy, conventional Edy's/Dreyer's (talk about overpriced!).