There is no perfect HN iPad app. I bought all of them but there is only 1 good designed from usability perspective, it's called Hacker News HD for iPad but it crashes after using it non-stop more than 1 hour or so without restarting app. Sometimes you need to delete and reinstall. So I tired of it, now I made a Homescreen bookmark for the website, it's the best way to browse HN.
I like news:yc on iOS. I've only used it on an iPhone, so I can't speak as to how it works on an iPad. Even if it was just scaled up, though, I think it's still a great app.