I always just the the best catagory for the item. Why pay twice the amount of fees for only selling one item?
If you are not sure about which catagory to sell in, then browse through the catagories that you are interested in selling and see if any like items are selling and then choose the one that is selling that item the most...
Also if you have more than one item that you are planning on selling then do some test listings to see which catagory that the item sells best in and then start listing your item in that catagory.
Just my opinion, as I know that some folks list in multiple catagories, but that can really cut down on your profit margins as you still have to pay the listing fees for every catagory that you list the item in....