Which is better, Terraria or Minecraft?

Minecraft.

They're both very different. I wouldn't even compare them, there's too much of a difference between them.

Terraria is more for adventures.
Minecraft is 3D and more for building.
Minecraft is more fun to me but Terraria has lots of more fun things to do.
Also you can install mods very easily in minecraft but not in Terraria.
Minecraft is cheaper.

This is opinionated but I think mine craft is a better choice there's more options and stuff.

I guess your friend is wrong.

Terraria is a 2D game which means it focuses more of platforming than the generally less severe terrain of Minecraft.

Terraria characters can move from world to world with their personal inventory, allowing you to build a huge city in one world and have giant battles in another.

Terraria has a larger variety of enemies, especially bosses.

Terraria has a wider variety of weapons.

Minecraft has more varied terrain types.

Minecraft is much easier to mod.

Minecraft has a wider variety of blocks to build with.

Minecraft is better in every way then terraria:
Minecfrat: 3D, Terraria: 2D
Minecraft: MODS FOR EVERYTHING!
Terraria: Not much variation besides Terraria and 2D games… :/

so basically minecraft is almost anything you want it to be…
you like building? Play creative.
you like surviving? Play survival, vanilla or modded.
you like RPG games? Play RPG modded server, you have WoW like, free roam grind, and just everything.
you like shooters? Play with a guns mod.
you like playing god and making landscapes? Play with mods XD
you like playing i don't know… Pokemon? Naruto? CoD? Hunger games? Zombie Apocalypse? All minecraft…