For long distance Kipchoge has the best form. Total relaxation of all the body including the upper body and the arms, face, palms, fingers (doesn't even fist his palms, shoulders relaxed. Hands close to the chest (it's more relaxed like this than in 90 degrees, most elites long distance don't have hands in 90 degrees, and who ever said that must have been a sprinter). No side to side movement of the torso. Minimal bounce that makes deep breathing much easier. Gazing a few meters down a head- this is a relaxed gazing, unlike all those that say you should look forward to the horizon. Most elite runners don't look to the horizon because it is less relaxing than gazing down a ahead, relax your eyes! Focused and not distracted (probably focusing on breathing rhythm)
Forefoot strike, but not extreme on toes like Rupp. Landing with a bent knee and doesn't full extends the knee. Leaning forward with a slight arch of back. not straight and tight. Beautiful to watch. Flawless. I advise any long distance to imitate that form.
Bekele's form is also beautiful but I can't learn and adopt anything from it becuase of a very high beck kick and sole faces sky (how do you that? ) and also a full extension of the knee (yet lands on a bent one)
http://www.athleticsweekly.com/wp-content/uploads/2015/09/Eliud-Kipchoge-London-Marathon-2015-1250x750.jpg
Relaxation!