Jan,
I bought both these books for my father and I'm now at his place so I'm able to take a look. Although I have not read either one, I can offer these very general observations:
Both deal with the same series of events in early 1944. The book by Nash is the larger one, with 370 pages and another 30 pages of appendicies. My Dad can't really recall whether one is better than the other but from my observations flipping through both, it appears the Nash book has more illustrations as well as text and seems to be the better book. There are many index references to the 5th and 11th SS Divsions in the index.
Not much I can offer but hope this helps a bit.