If you are a beginner and intend to keep breeds like Rottweiler, Gsd, Dobermann Pinscher, it's advised that a female should be kept as they are calm in nature and easy to be handled. Male dogs during adolescence can become overly protective, hyper-active and excited, and agile which a beginner may have problems in dealing with.
Females come in heat only two times in a year so I wonder how much dirty they can keep your house in a year. What about a male trying to mount on your legs in front of a guest. Well, all males do. What would you prefer a male or female???