Lippy,
I had the same three choices a few months ago when I was in the hunt for a new road bike. I ended up with a Synapse 6 with the all Tiagra groupset. I have found the bike to be very very good in terms of comfort, speed, smoothness and handling. The CAAD 9 was very fast but also a bit too harsh for me. The only change I have made to the Synapse has been replacing the stock crap saddle with a Specilaized Alias. Good luck!

P.S. I believe you are also looking at the same LBS I did when I bought mine since the prices are identical to what I was quoted for the 3 choices. FWIW, I weigh 240lbs and am 6'2" so that should give you an idea from the comfort standpoint of the Synapse.