I would definetly recomend keeping 2 rats together because rats are very social animals. I personally prefer females, but it depends on you. If you like a rat that will sit on your lap and watch a movie with you, you would probably prefer a male. On the other hand, if you want a rat that will play with you all the time and is always exploring, you probably prefer a female. Rats almost never bite, if you handle them gently. If you treat them gently, they will always love their owners and be completely loyal. If you decide to keep 2 males together, I hear that they can become territorial.