cp vs. mv: which operation is more efficient?

I find myself moving reasonably large amount of data (20+ GB) from one directory tree to other. Often times they are on the same filesystem but sometimes they are on different ones. I do cp just to preserve the original data just-in-case. Once the copy is done I delete the original data after verifying that the data has been copied alright. Sometimes I just do mv if I feel too lazy to clean original data afterwards. However, I am wondering, from purely technical point of view, which operation is more efficient? Why?

Copy text from one terminal into another

I am logged into ssh to a university account from my home computer. Then I find a file that I want to copy onto my local system. So I open a new shell terminal and am about to use scp to copy that file onto my system. But the path to the file on the system I am ssh‘ed into is long so I select it with the mouse and then paste it with the mouse into the other locally connected terminal.