The problem with duplicate finders isn't getting one with the features you need, Mubs, it's getting one without the kitchen bloody sink grafted onto it! Most of them are so full of clever tricks and bells and whistles and handy added extras that it's quite difficult to just do what you need to do. I do use one that seems pretty good, the name of which escapes me just now 'cause I reinstalled a while back and haven't needed it yet so it's not installed. But I only use that one now and again; mostly I go to the other extreme and use a tiny, ancient little thing with a UI that is beyond primitive.
Why on earth would you want to use something as badly finished as that? Simply, because once you get past a couple of annoying UI errors (of the kind you would expect in a 0.44 release) it works perfectly well and you can actually understand how it is going to decide things. I better explain:
Dup finders have to have some way of knowing which file is the dup and which one is the original, and very often it really does matter which one you delete. Some make you decide that for every file individually (hopeless!) or by using some arcane ruleset, always with your heart in your mouth in case you have misunderstood the rule and destroy something important. Dupfinder is refreshingly simple, almost mindlessly simple: it uses alphabetical order. That's it; nothing more to know, no switches to double check. The first file (alphabetically) will be deemed the "original" and all other copies are "duplicates". When the search is complete, right click on the duplicate list, select "delete all duplicate and empty files", and confirm.
Folder names take priority over file names, so if you want to prioritize folder MY_STUFF\ first and only keep files in A_LOT_OF_STUFF\ if they are non-duplicates, simply rename it (for the moment) to ZZZ_A_LOT_OF_STUFF\. Do the same with other folders - you might have a ZZY_MORE_STUFF\ and ZZA_LOST_STUFF\. Even when you are tired or distracted, this dead simple brute-force approach means it is pretty hard to make a bad mistake. You will be keeping everything in MY_STUFF\, then deleting duplicates in ZZA_LOST_STUFF\, ZZY_MORE_STUFF\, and ZZZ_A_LOT_OF_STUFF\ in that order. Even when you are tired or distracted, this dead simple brute-force approach means it is pretty hard to make a bad mistake. (Oh, and be sure you tick the box labelled "Fast CRC checking"; it speeds things up by about 10:1. No downside that I've ever noticed.) Works on any Windows version.
If all that is too Spartan for you, this is the other one I use now and again, when I can be bothered figuring out the controls and need something more advanced. http://www.digitalvolcano.co.uk/content/duplicate-cleaner It's pretty decent. Not that there is a free version (for non-commercial use) and a 15-day trial pro version. I just use the free one.