In the grand scheme of a 162-game season, who pitches on Opening Day doesn't matter that much. Even the outcome of that game is largely insignificant.
Still, being picked to take the ball on Opening Day is a big deal for pitcher, as it signifies they are the top pitcher on their staff.
Fun fact: Tom Seaver holds the MLB record with 16 Opening Day starts.
With 25-man rosters more or less set and Opening Day starters having been named for all 30 teams, here is how I rank each team's top starter.