Good Orchestration Book?

I am trying to decide on whether to buy Adler's "The Study of Orchestration" or Kennen's "The Technique of Orchestration". Can anyone here reccommend one of these? I am considering Adler's book since it looks more thorough. But Kennen's book looks promising too.

I have the latter book and I was pretty pleased with it. I haven't read Adler's so I can't compare the two, but Kennan's book was a great asset for me since I knew nothing about the orchestra prior to reading it. It very thoroughly explains each part of the orchestra in as many chapters as necessary and the material is divided up very sensibly. It gives you the ranges of each instrument and a decent description of how they sound in different registers (a very important thing for woodwinds) and plenty of information on the different special techniques (bowing techniques, mutes, distressed piano). There's even a chapter on infrequently used instruments and a short one on non-orchestral ensembles. And throughout the book there are plenty of excerpts from scores given as examples of the different subjects discussed. Also lots of detailed information, little tips and tricks so that the book isn't just a lot of basic facts you could look up on wikipedia. The authors give plenty of advice on handling different situations where orchestration becomes a little tricky. Overall, it was a very good resource and still is, since I haven't got everything chiseled on my brain that I need to know.

Thanks for the review KJ. Anyone read Adler's book? I think I heard his book mentioned here.

Adler's book is one of those "must have" books for a composer. Both texts are pretty similar to each other, and both have the same amount of detail. I prefer Adler though, I think its better organized and has better score examples...but that's my opinion. 

While I have neither book, I found this helpful page comparing the two as well as supplying many alternatives.

http://wiki.youngcomposers.com/Orchestration:_Texts

I've been lurking anonymously for several months now. I'm also aware this might be necroposting, but I just had to create an account to add this book to the list: "Instrumentation and Orchestration" by Alfred Blatter. It's incredibly detailed and thorough in its coverage of different instruments. Its coverage of orchestration is a bit on the small side, but I've actually found that side of the book to have helped me the most, especially its section on arrangement.

Blatter is perfect for instrumentation. I have studied that in Uni. Now, my orchestration skills are lacking, but I think I'll read Piston's work. 

I suggest Blatter + Piston being the perfect combo for an all-encompassing instrumentation/orchestration coverage.