A clone will create an exact duplicate of the original drive - files, partitions, layout, and all. Generally you only need to do this for boot drives, where idiosyncrasies of bootstrap layout may make a difference. One peculiarity is that if you clone a 1 TB drive to a larger drive, it will be set up as a 1 TB drive. You will have to manually expand the partition(s) to use the rest of the empty space (some cloning software will do this automatically).
An image is a backup. It converts a partition (sometimes multiple partitions) into a file which holds the contents of that partition. This is not what you want unless you want a manageable (immutable) backup. Depending on the image creation program, certain files (e.g. OS or temporary files) may be excluded from the image.
Since you're just talking about data files, copying a disk is probably what you want. But be careful to set certain flags so you don't miss hidden/protected files, and be sure to use the verify option to make sure copies are clean. The Windows copy command is not very good for this because it dates back to the DOS days. Xcopy is probably better, but is still a command line tool.
Instead, you may want to look at GUI copiers. I personally use TeraCopy 2.3, but it's got a few bugs and I don't recommend the 3.0 version. One advantage of these is that they're pretty good about skipping files you've already copied (if you enable the verify step, they will check previously-copied files to verify they're a clean copy of the original - important because the file which was being written at the time of the failure can sometimes exist as a partial copy). So you don't have to worry about the failure problem USAFRet mentioned.
http://www.topbestalternatives.com/supercopier/
And yeah, copy first. Manually delete later after you're satisfied the copy was done cleanly.