Of the two, I would go with the Giant because it has the newer 11 speed 5800 105 group. Also has 105 cassette with 11-32 where the CAAD 8 has older 10 speed 105 with Tiagra cassette 12-28. Guessing it's pretty flat where you live so having the 32t gear is not a big deal and you might actually want closer spaced gears. Other factor is the Defy is slightly more relaxed geometry. So ....test ride them both and see which feels better? But if I was going to pay that much for a new 105 bike I would want the 11 speed.