Which first person shooter is the best Call of duty, Battlefield or Medal of honour

It depends on what you want from a first person shooter game.

• Call of Duty (CoD)- Best for fast paced gameplay, arcade-style action with a strong focus on tight gunplay and cinematic campaigns. The multiplayer is a solid feature in any Call of Duty game and is highly competitive, with modes like Warzone offering battle royal experiences.
• Battlefield - Best known for Vast scale warfare with destructible environments, vehicles (tanks, jets, etc.), and advanced tactical gameplay. 
• Medal of Honor - Was the original first person pioneer of military shooters but has fallen behind. The earlier games (like Allies Assault) were too notch classics, but the franchise hasn't kept up with CoD and Battlefield.

If you want non stop heart pumping action go with Call of Duty.

if you prefer massive battles with vehicles and teamwork, go with Battlefield.

If your goal is to fight in classic WW2 battles maybe Medal of honor is for you.