Warchild pretty much hit the nail on the head. Just do a ton of research. From my experience males tend to be more dominant then females but that can vary from dog to dog. You really need to know what you are getting into before jumping into this breed.
I have 2 males. My one just turned 13 in July (old for a rott). He was a very dominant male through his younger years. Now hes just relaxing in his golden years.
My other male pictured below is less dominant, a great watch dog, and a real sweet heart. He just turned 7 on New Years.
Good luck with your decision.
