Sometimes I like to get the point of view from the original folks, Melomed, Gorbach, Berger, and Bateman. Sometimes it is good to hear from the original creators, but I admit it took me about 4 times reading the book to understand it all in and out.....the XML/A, AMO, MDX. For me it was the best book to know what is going on under the covers :-D
For a developer I think Ferrari, Webb, and Russo give the best view from many different levels.
Bottom line for me: SSAS is a majorly complex piece of software, and it is good to get as many viewpoints as possible if you really like it.