Glomgold has very few appearances and even fewer that are written well, but those that are, god... Perhaps my favourite is his first appearance ever, Barks' "The Second Richest Duck", which portrays Glomgold as Scrooge's darker version and shows the biggest thing they have in difference: family. The ending where Donald's nephews are helping him to walk back is heartbreaking and emphasizes just how completely alone he is. (He might be the least villainous and most like Scrooge in that story. He became darker later.)
Rosa's "The Son of the Sun" and "The Last Lord of El Dorado" are very different but also excellent uses of the character. I don't remember much of Ducktales, but I think he was a much more straightforward villain in the show than in comics. Rosa's Glomgold is quirkier, wittier and more on level with Scrooge than Rockerduck ever was, IMHO. I do like Rockerduck, though, he's just in a completely different league, depending a bit on the writer, of course. (I'm a Finn, so we get like every Disney comic published except for the ones I want and have to buy from Italian eBay after years of fruitless waiting.)
Yeah, I'm biased, too. I want to write and draw just one Glomgold story someday and possibly offer it to our duck publishers as a freelancer if it's good enough. But mainly I just want to make one.