
Prefgerably not another Bull breed, as from my understanding they should not be left together unsupervised, as if a game gets out of hand it can end in a bad fight with neither backing down.
I would get a member of a medium size breed that is known for being very sociable non dominant with other dogs.
Archer on this site has a staff with my breed. I also know that many Gundog breeds even the Stud males can be happily kept toggether in mixed sex households.
JMHO