Panthers, because the Oilers have not faced as much heavy hitting pressure, and certainly not as dirty a team as Florida. Dallas was in pure pacifist mode afraid to take a penalty, as thats how the Oilers won the series.
When McDavid tries to pull his x-checks in the corner (which he does often) with no response vs the Panthers, he'll get flattened.
Every shift, someone is going to hack and slash him, so, either he'll win a medal for diving, or realize some teams dont care who he is.
This series will show what McDavid made of, and it can define him if he can overcome it, but, if he cant, it will be the future recipe to stopping him in the playoffs.