either or, both can be super sweet and calm if handled from a young age. There may be a slight trend towards males being a little more laid back but in all I have both males and females who are just big love bugs!
My mother had two males--had to keep them in separate but nearby cages b/c they would fight otherwise. Males can be neutered, but neutering can actually make their eyes fall out (not kidding!)
Now has two females (whom are next to me on the coffee table) and they can be in the same cage.
For personality, of two males, one was friendly, one wasn't.
For females, one is friendly, one isn't.