Couldn't find that specific model C'dale. 2008? Is the frame alloy or carbon?.
I own a full carbon SuperSix and a Defy 1(pretty much the male versions of the bikes you're looking at) and the real question is what you're looking to do with it. A performance/racing machine,or a daily rider? The Cannondale would make a better racer;it would definitely be worth upgrading the components to higher levels and competing on it. Plus they're not making all the models in the US amymore,which may allow it to hold mroe value(I would not worry about warranty issues with Cannondale BTW). But the Giant will take wider tires(by road bike standards),a rear rack,and even full coverage fenders if you do a little MacGuyvering. So if they both fit you,I'd choose the one that's right for how you're going to use it.
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C'dale BBU('05 and '09)/Super Six/Hooligan8and 3,Kona Dew Deluxe,Novara Buzz/Safari,Surly Big Dummy,Marin Pt Reyes,Giant Defy 1,Schwinn DBX SuperSport,Dahon Speed Pro TT,Brompton S6L/S2E-X
