I own a Look 595 Ultra. That bike is way more comfortable than the CAAD9 I own and the CAAD10s I have test ridden. No comparison. It is something about the lugs, the high modulus carbon used and the integrated seat mast with elastomers. The CAAD10 is not even comparable in regards to comfort. The 595 Ultra is like being in a Cadillac compared to the CAAD10. YMMV.
Each person will have their own opinion. The CAAD10 is a great bike. No doubt. But if comfort is #1 I would personally look elsewhere. Better yet take it for a test ride on your favorite route. That will let you know for sure.
Moving from the Look to the CAAD, the only thing I lost was some Italian sex-appeal. I gained some sweet Americana though. In all seriousness, I rate the CAAD superior in every way. Being aluminum I thought is was going to be harsh but I was pleasantly surprised and would choose it first every time. The geometry was also a better fit for me overall.
Except for the fact that the Look is French and not Italian.