Ours only used ground nest boxes, so I would go with those. Wood ducks and Mandarins are a little different in that they usually nest in trees, so that's why they prefer mounted (raised) nest boxes.
Oh, and I don't mind the questions! I'll help in any way I can. Laysan Teals may not be the most colorful ducks, but they are still beautiful and fun nevertheless. I had one who I had to hand-raised that was the sweetest thing ever! I was so sad when she was transferred to another zoo for breeding purposes. :/