Most important thing is to be choosy about who you buy from
There is no way of knowing how any animal will develop,either psychologcally or physically.
But you can see its parents if the breeder is reputable.
If the parents are healthy and happy you have a good chance of a healthy and happy youngster.
Big,small,fast slow.In my experience all ferrets love bolting rabbits .
I prefer small ferrets as they take up less room and are less inclined to tangle my nets.