"The Yankees are the best baseball team in history." is the opinion, because it shows the personalized emotions toward the team.
"The Yankees play in the greater New York City area." is not an opinion because it is telling where the Yankees play.
"Yankee Stadium sells hot dogs." is not an opinion because it tells what the stadium sells. If they had said "The hot dogs' Yankee Stadium sells are really good" it would be an opinion.
"Babe Ruth played for the Yankees." is not an opinion because it tells what team Babe Ruth played for.