Well twice this morning I lost lengthy posts on line, I guess that's gods way of telling me I talk too much! I did go book by book comparing both for you bakerbebe....but lost it.
Quick answer, get "Death by Chocolate" first it had the most hits in it. All of his frostings, ganches and mousses are terrific (with one exception, his simple chocolate mousse isn't great). I never made any of his icecreams, both books have several recipes for them. I also am not crazy about his baking (cakes, cookie and brownies), they tend to be abit dry (but still good, just not perfect), so underbake them or use your own instead. BUT he is brilliant in his layering and fillings. If you do buy any of his books I can give you notes on which items were great and which were misses.
His cookie book and his latest chocolate cake book were the ones I wouldn't buy unless I had alot of money burning in my pocket.