Can't speak for Cockers, but I had five Scotties, all bitches, and they all got on brilliantly, ruled by the paw of iron by number one Scottie. I have had two boy dogs on two occasions, one set of them Cockers, and I wouldn't do it again, but one was a rescue, with issues. But that's just my experience, others will have different ones. I have just the one boy now, and if I was to get another, I would get a bitch.
Lesley and Dylan