If “he” actually is a major league baseball player, both versions would be acceptable. Otherwise, “would be” is needed. For a “spectator”, the thought of being a player would be supposition.
lucas21cWhich one is preferred between 'would be' and 'is' in the sentence?
The one that tells the truth is the preferred one.
"is" is preferred if he is a major league baseball player and he means his being a major league baseball player is exciting for himself, of course. You must say what you mean.