7 Answers

Male dogs are not necessarily more aggresive than female dogs. My tip for buying a large breed dog would be to have a good look at the parents and their past history if available.

Actually it's the females that are more aggressive. 

I had a female who was far more agressive than any male I have ever owned.  If you are concerned do not buy the Alpha in the pack... male or female.  I have had the good fortune to work with animals for the best part of 30 years and I have never met an agressive Great Dane.  This isn't to say that they don't exist.  The key to buying a solid and healthy Great Dane is buying from a reputable breeder.

One place to look is the GREAT DANE LADY... she knows it all.  www.greatdanelady.com

I think it is according to how you bring up the puppy how disposition will be not gender.

Females are more aggresive due to being more protective of the owner/family

All dogs that are pets only (not to breed) are much better and docile if they are spayed or neutered

My family was in the front of the house in dark, cold December. I was in the way-back bedroom wrapping gifts. My female German Shepherd was standing just outside the door. I looked at her and was disturbed by the look in her eyes. She started a low growl. I shut the door and that started more growling. LOUD. I called for my family. No one heard the commotion in the back of the house. I had to go out the window and it was difficult, slippery, freezing.  No more female Shepherds for me. In fact, no more dogs. 

This dog was new to our family and she had  congenital hip dysplasia. I can guess that she was in a great deal of pain and we hadn't been warned.