I have similar feelings as Denny with Citra. Nice when treated like a spice, but when it's a dominant flavor, it just kills a beer for me. I try and use just enough of it in IPA's to get a hint of flavor, but not so much that I can pick out the Citra flavor on it's own. I've found it can also overpower everything else. Even when I use it in smaller doses compared to other hops. Definitely one to be careful with.
3 months ago I would have said Comet. Then I had Russian River's single hop APA (Hop 2 It) made with it, and realized I'm just doing it wrong.