My Ex's Nephew keeps several ferrets as pets, and goes 'rabbiting' with them. They are the largest, and only domesticated of the 3. Size/weight-wise next comes the stoat with a black tail end, then the weasel - although large weasels can be bigger than small stoats.
Ferrets can be very affectionate, especially with their owner if handled regularly. They are cheeky and playful if a bit bitey. Not suitable for children - these ARE predators. One thing that sticks in my mind is that the female must be mated every time she comes into heat or she is likely to die of shock of some sort. Keepers usually have neutered males for this mating - it's the act, not resultant pregnancy that saves the female's life!

Dave.