Race bikes are built with the intention to squeeze out the most performance possible.
They are split into two distinct categories, Aero and Lightweight. Aero bikes are designed to be ridden at maximum speed and work best on flat/ungelating roads. Whereas Lightweight bikes are designed to perform best when climbing and ungelating terrian.
So, if you love a Criterium and flat our speed is your thing then go for Aero or if you prefer all round agility, long road races and mountain passes then go for Lightweight.