Well, I think the Defender is the most fun ship in the game.
For utility, I have to give the prize to the shuttle, but, well, we're talking about Defenders and shuttles here, so utility obviously isn't part of this.
I really don't think shields are an issue with either of these ships. They really don't have any.
The Defender has one actual use: Because it's so fast, especially after it's modified (yes I'm sick enough to spend 430,000cr on a 90,000cr ship), it can be used well for escorting or running criminals or basically any mission where sheer speed can help you. It's easily fast enough to outrun and outmaneuver missiles.
Personally, I prefer the Defender. Neither of them's really worth much, though, except as a toy.
(You enjoy silly questions, don't you? )