All three bikes are good buys, racing, sport training or just plain riding for pleasure. I have the CAAD 10 and ride it for my exercise and training. Synapse and Super Six are excellent bikes, just consider how much you want to spend, to me. What type of riding do you mainly do? If you can afford the Super Six at which ever build level you choose, go for it. For rough roads and day long rides like a century or other Sportive rides the Synapse is hard to beat.

Milkbaby's reply about geometry should be a stickie IMHO, it is well put and accurate. Read it and take this into consideration, too.

Bill