I believe most builders would agree with Ken that wood type is a much more minor factor in determining the tone of a dulcimer than it is to the guitar family. That said, I would suspect that, other factors being equal, the dulcimer with the redwood top would have a slightly more mellow tone than that with the sycamore.
Hearing a dulcimer before purchase is certainly the better way to choose but, if that's not possible, Ken's advice is pretty solid.
lynn mc spadden once told me that different tops needed to be of a different thickness. i think he was right
The type of wood is pretty far down the list of things which affect the tone of a dulcimer. Not that those two dulcimers would not have two different sounds... just that the difference in top wood will be for all practical purposes, not distinguishable. Especially in this case since they both have the same wood for the back and sides.
IMHO buy the one that appeals to your eye.
