The Simple Guide, covers less but emphasizes some things more than the others I would think are very important. While I think Aquariums For Dummies has more info and reference stuff that will be used if you get really into the hobby. For the true beginner with freshwater fish I would recommend The Simple Guide, but if you are only going to buy one book for years with multiple setups I would use one of the others (You & Your Aquarium, or Aquariums for Dummies).
But I do think anyone into fishes would enjoy going to the library and picking up The Complete Aquarium. It is an older book so I think the best option really is the library. The library is free and is under utilized in the U.S., I am not sure where you are though. <shameless plug for libraries>