The trains system in Morocco is very reliable even in 2nd class. The fare difference to an upgrade to 1st class is not huge and it is worth specially in night train. There is no security issue and it is very safe. You do not need to book in advance, when you arrive to Marrakech you go to train station and you buy your tickets.

Personally I would avoid Morocco to begin with. But yes as mentioned before, the trains are comfortable and reliable :)

The trains are great and reasonably comfortable, particularly if you get the 1st class ticket. Baggage has never been an issue: you can take more than on the airlines. I do recommend booking online if possible in advance if you're traveling on a holiday weekend or other busy time as they will occasionally sell out. Rare, but it happens. Also agree with Mich: Casa isn't much fun. Marrakech, Fes, Rabat are all much nicer and have their own identities.

Just 3 words: Cheap, comfortable and reliable! Just Casablanca isn't that interesting ...