What's your favorite Minecraft command?

It's very common to play the game in survival or creative mode, and access commands to do things like give blocks/items (/give), teleport to players (/tp), switch the gamemode (/gamemode), set your spawn point (/setspawn), spawn your own mobs (/summon), enchant items (/enchant), add effects and modify their duration and amplifier amount (/effect), give yourself experience (/xp), and so on.

Which Minecraft command is your favorite, and why?

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I think it's pretty hard for me to choose any particular one, because I've had a lot of fun with many of them. My choices would probably narrow down to /enchant and /effect.

But I think I'll choose /effect as my favorite since I've had a lot of fun with this one and I feel like you get more out of this command than you do out of /enchant; like playing on one of my friend's LAN servers with commands turned on, I pretty much gave myself OP effects (like speed, invisibility, strength, night vision, absorption, saturation, health boost, and regeneration) and just snuck up on my friend and took him down in one hit, which was funny. Plus I get to be OP against every mob, when I have those effects turned on, so it's pretty fun to play around with in survival mode.