Generally, the top of the line race frames, with as low a head tube as available. Fr'instance, Trek riders use 7-series Madones in H1. Cannondale riders used SuperSixes. Specialized riders use S-Works Tarmacs and Venges. Some of those guys get special builds, which generally means longer top tubes and shorter head tubes. Often, the rider can choose between the sponsor's "aero" and lightweight or general purpose bikes (Venge vs. Tarmac, Scott Foil vs. Addict, etc.)
For cobbled classics, many sponsors provide "endurance" frames, but these are generally special builds having longer top tubes and shorter head tubes. The Trek Domane "Classics Edition" is an example, perhaps the only one, of a true race "endurance" build that is in a catalog. Race versions of the Specialized Roubaix might be available if you know a dealer who will contact his district rep for you. Scott-sponsored teams get a special long-and-low Solace, and Cannondale teams get a special long-and-low Synapse. Giant riders get a Defy with a cockpit geometry similar to the TCR or Propel.
It's interesting that the front end geometry of the race Domane, steeper head tube and longer fork offset, flies opposite of Trek's general long-trail philosophy shown by Madones and civilian Domanes.