Generally, I would opt for one of each sex. Just make sure you have twice as many hides, so the less dominant snake doesn't have to choose a less suitable hide.
I keep two watersnakes together and I have 4 different hides, 2 groups of 2, so that each can choose a warm hide or a cool hide depending on preference. But they get along so well, they usually crowd into the same hide, even though there is an identical one actually touching the one they're in.
Rome did not build a great empire by having meetings, they did it by killing all who opposed them.