Which type of Rat???!!!! HELP!!!!!!!!!!!!!!?

Well I maybe getting a rat but my mom said I have to wait until the summer is over cuz it will get hot in my room and it will smell REALLY bad cuz I already have a Black Bear Syrian hamster named Sammy in my room. I love him to death, and Sammy is 5 or 6 months old. But anyway, if I get a rat, which type??? I know there are a lot of different types and colors, but I don't know which one to get. Can you tell me which one is the best type and give pics, and should I get 2 or 1 ??? THANKS!!!!!!!!!!!