I think it will boil down to the personality of the dog you currently have - whether they prefer the same or opposite sex. Take your dog out to areas that have a lot of dogs and see if there is a trend in which sex he prefers.
Either way, eventually they will warm up to each other. Lauri had a dog that hated all other dogs. She brought a Samoyed into the house and her other dog gave her the cold shoulder for about a year and then gave up and started liking her.
If you are talking about bringing two puppies in at the same time, I don't think it will really matter because they will grow up together.