I would say the night elves have the advantage,
They're armies have far more experience they have access to a greater range of powers. I Mean Night elves have fought in multiple wars almost single handily and won them, It even took the entire horde and them diverting the Night elves army for them to win the War of thorns.
Where as the history of the Blood elves has been them relying on the Alliance to survive and now the horde. Honestly I don't think their is even a contest.