The best travel guide that I ever had for Morocco, acquired back in the 1980's, was a very old blue Michelin "Guide Bleu" which I suspect dated back to the mid 1950s. It was great because it went into huge detail about matters and places that were real "history" by the time I read about them. Like many things, I loaned it out but it never came back.... :-)
These days I evidently have a very much reduced attention span, rather like a goldfish, and find that the Dorian Kingsley "DK Eyewitness Travel" guides suit me perfectly (see traveldk.com ) as they contain profusely illustrated (or photographed) short articles in colour about all the good things to see at my destination. The most recent one that I purchased was their specific one for Marrakesh - ideal!
I like the carefully researched detail in the Lonely Planet guides but just appreciate the graphic 'plus' of the DK Eyewitness Guides.