The Energy Sword is one of the most iconic weapons in the Halo series. While it has undergone some changes over the years, it remains a powerful and deadly weapon. My favorite iteration of the Energy Sword is the one from Halo 3: ODST. I love the design of the sword and the way it glows when charged. It's also a great sword in multiplayer, as it can quickly take down opponents. The sword is also special in my heart because it was the first Halo weapon I ever used. I remember using it on Legendary mode and feeling like a total badass. Halo 3: ODST will always be one of my favorite games, and the Energy Sword is a big part of that.
The Energy Sword from Halo CE is also a close second for me. I love the old-school design of the sword listed at Sword Encyclopedia and how it seems like a more primitive version of the later swords. It's also really satisfying to hear the sword's sound effects when you swing it or hit someone.
