I think the Defy is the best bike out there. I've raced mine, commuted and ridden sportives. It is the pefect all-rounder. The alloy one can take guards and a rack. That said, Son1 has a CAAD8 Tiagra, and it is a fine bike that will also take guards but not a rack. He rode 1000km without any issues today from a pretty low base. The stock saddle is dreadful and the wheels are heavy - as will all the others be at this price point.
Forget ideas of comfort or sportive bikes, they are road bikes. My defy has 0.5 cm of spacers and my TCR has about 2.5 cm. The bars are in the same place, and so is the saddle. I've raced them both and felt little difference.
If it were me, I'd buy the Defy 1. The CAAD8 is lovely, but you need to be a 15yo Peter Sagan wannabe. And matching bar tape and saddles to the team livery is not a cheap option for aftermarket goods. But the two bikes are the outstanding choices at the price point.