I agree with Jim; fit is most important.
I bought a really great Caad8 on sale and found the frame couldn't be made to fit. I went to a different bike shop, was expertly fitted 9to a steel with carbon forks frame) and swapped the fancy gear over and sold the Caad8 frame to support the Jimmy Fund. 20,000 miles alter I still love the ride.
I have bikes with Tiagra, 105, Duraace and Campy. Wheels are more important.
Unless you are poor Andy Schleck today, weight and function differences in shifting gear aren't all that important and they all work. The higher the price, the nicer it is but a good fit, nice wheels and a nice frame are more important than the shifting gear. If the ride is the same and one frame weighs a pound more go for the cheap frame and get clip on peddles and shoes.