Factory HD Manual & the Corresponding Parts Catalog are must haves. The Parts book shows the exploded views which really helps.
I agree with getting them both. Great to have the exploded views in the parts catalog and being able to go into the dealer with the part number you need is a time saver. Factory manuals are the bomb digity!!
I would buy the hd manual...its the best available...but still not all that good...for example I tried to look up how to replace the rear turn signal lamp assembly on my 2000 sportster ....the hd manual didn't have it even in there...