Pretty much what Azie said. Actually, I suppose your preference in Minecraft vs. Terraria is significant because of what it says about you as a person.
Most of my friends seem to prefer Terraria because it gives them goals to work toward, while in Minecraft there are no goals, really. They love all the cool weapons and armor with infinite durability and could never really be bothered to figure out how redstone logic works. I don't really want to spend most of my time killing monsters though. I want to build, create, and inspire others to do the same, thus I prefer Minecraft.
One of the reasons Terraria has more content is because most of it is focused on finding new ways to kill monsters, while Minecraft tends to only implement new resources if they're unique or pragmatic when surviving or building machines.
Course, there are probably mods to turn one game into the other by now. Terraria always did feel incomplete because it lacked creepers.