From my point of view is "Add" the better option. So you have only one copy of the picture files. It is easier to handle.
The better option is the one that works best in your workflow. Do you want to automatically reorganize (the Move option would do the same as Copy, but without creating a duplicate) or do you want to retain your existing organization and rearrange them yourself? Whatever you do, just make sure you have backups!
The problem is my original photos went into picassa, I named the photos and a folder was created. Picassa copied all. Some folders have multiple events or subjects in them (ie.Stacey's birthday, July 4th party and fireworks, sunsets and flowers) . So ideally i want to separate those out for now, using a parent folder for the year, everything else for that year underneath. I did read a thread about "adding" that is making me stop in my tracks to think about this. When I import from my card, it is pretty straight forward,folder on HD identical to folder in LR catalog. (Yes I know they are one in the same )