adopting a second cat: right match

[ubenclagen]

Hi - this is the first time I've posted here. I have a cat that is two years and two months old. He is part Maine Coon. When he is active, he plays with his toys, runs around like a nut, jumps the walls, and plays rough with us. In other words, he can be a bundle of energy. I've had cats all my life, but only one at a time. My other cats were so territorial, they would hiss and growl if any cat came near our windows. My current cat does not do that; cats will visit on our deck and my cat will excitedly paw at the sliding glass doors and jump up and down, no hissing or growling at all. I think he wants to play and perhaps would welcome a cat friend into our family.
Now, my question is: what kind of personality should the other cat have? My vet says that my cat's age and rough-housing indicates that an older kitten, 6-12 months, who is a little more docile, would be the best match. That way my cat can establish his dominance in the home. She said getting another cat that was like mine would lead to conflict. However, this weekend I was looking at cats at an adoption day held by a rescue group, and they said "no way!", that the younger, new cat would retreat and regress. They said that I should get an active adult cat that can hold his/her own while rough-housing with him. Of course, they had a 3 year old female there who fit that bill, so maybe they were just encouraging me to adopt her.
So now I don't know what's right! Any of you who have experience bringing a second cat into a house like this, could you tell me what you think would be the best match and why? I intend to introduce the new cat slowly by giving him/her a room to itself, and slowly letting them into each other's territory etc.
Thank you for any help you can give me.