Here's my lowdown on these two guys:
Skating ability: McDavid's blazing speed, agility, and edgework are ultimately greater than Eichel's. However, Eichel is a strong skater and has lower body power that gives him such force when he strides. Not to mention his skating is very smooth as well.
Puck skills: Their puck handling/passing skills are almost identical as they can both make incredible plays at such high speeds. I wouldn't knock either of them in this category but McDavid however, I would have to give the edge to for passing ability.
Shot: Eichel's wrist shot is very deceptive and I think he has a better release to get it off. McDavid's shot is somewhat underrated. I can't comment on their backhand shots, nor can I with their slap shots.
Vision: Both have masterful on ice vision, almost like 360 degree vision, and they can execute deadly plays very, very accurately.
Intelligence: McDavid has top tier, elite hockey hockey IQ- able to read plays before they unfold, and this is seemingly where McDavid gets his high marks from. He does this better than Eichel, though Eichel isn't the player you want to knock in this category either.