I'm trying to decide on a new road bike and I'm hoping to get your thoughts. I currently weigh 265 lbs and would like to get down to about 200 lbs. I'm 5' 11" tall. The priority for this purchase is to lose weight and to be able to ride for 2 or 3 hours at a stretch.
If you are riding for 2 to 3 hours at a time and watching your diet you're going to lose weight. I haven't compared the bikes, I do have the Roubaix and have been happy with it. I was around your size when I first got it and didn't have any problem.
Common advice is ride all of them if you can and see if you suits you best. The other consideration is what LBS do feel like you want to do business with after the purchase. If these two match you are in great shape.
Most bikes at the same price point are going to be pretty comparable if you are buying new.
2013 Trek Domane 4.5, 2009 Specialized Hard Rock 29er, 1989 Cannondale w/Campy Nuovo Record Components (mostly anway, now just on the trainer) and Easy Racer Recumbent (home made from plans)
I agree with dbikingman. The components list will be similar in quality if not brand between bikes of certain price range. Designers have differnet ideas and one may just feel better. Best advise is ride all you can and get the one you like a a good LBS.
Ride them and see what feels best. Personally, I'd probably go for the Giant Defy. The LBS here really believes in Giant and usually says that for the price you get a better deal than with other bikes out there.