During a recent visit to Morocco, hitchhiking across the whole of the country from north to south, I used the 8th edition of THE ROUGH GUIDE TO MOROCCO (published October 2007) and its main competitor, the 2007 edition of Lonely Planet Morocco.
For the independent traveler who wants to explore Morocco in depth, the Rough Guide is clearly the best option among current guidebooks. It is much more detailed than the Lonely Planet, covering charming smaller towns left out of the LP and other guidebooks. If you are planning to go from Morocco to Mauritania overland, the Rough Guide is extremely helpful. While Lonely Planet didn't even update their Western Sahara cover in the latest edition, Rough Guide gives information on the new opportunities for those without their own vehicle. (Be aware, however, that the Mauritanian visa must now be requested in Rabat, not in Casablanca as RG advises.) Unlike Lonely Planet, which is now abandoning its traditional demographic of backpackers on a budget, the Rough Guide has as much guidance for shoestring travelers as for people with money to spend.
If you are curious about Morrocan history and culture, the Rough Guide makes other guidebooks look like they were meant for rude and insensitive package tourists. It contains a hundred-page supplement which not only explains the whole of Moroccan history and its prominent writers and artists, but it even gives some short pieces by Morrocan traditional storytellers. The Rough Guide does a good job throughout of trying to put tourists in contact with the locals. The hammams (Turkish-style baths) listed in the book are those frequented by ordinary Moroccans, not expensive spa-type locations as in other guidebooks. I was unhappy, however, with the Rough Guide's mention of hitchhiking. While it does mention it as an option, and doesn't try to scare people away from it, it suggests that it is difficult and requires payment. That's odd indeed, since hitchhikers consider Morroco one of the easiest countries on Earth, and my usual waiting type was just a couple of minutes, and I didn't have to pay a dime.
If you are an independent traveler, the Rough Guide is probably the only book you need. Lonely Planet does have a whole section dedicated to trekking, but even for those keen on trekking this may not be worth it. All in all it's funny how the Rough Guides, held in scorn for so long because they contain ads and are published by a major corporation (Penguin), now seem the best guidebooks for solo shoestring travelers.