I believe you've posted in the wrong forum, but I'll try to answer your question.
First off, are these two rabbits fixed? I presume they are otherwise you would have a ton of babies on your hand.
Since your rabbits are currently fixed, if you want to get a baby, honestly, the sex won't matter in my opinion. It will depend more on what your current rabbits will tolerate. However, note that if you do successfully bond the baby with your current two buns, the bond will likely break once the baby grows up to reach sexual maturity. You will need to work on rebonding them once you have the baby fixed, and it can't be guaranteed they will get along afterwards.
Typically, I would advise you bringing your rabbits to a local shelter or rescue and meeting other adult fixed rabbits on a bunny date to find one that can easily get along and join the group. Hopefully my advice is helpful.
As a side note, what do you mean chase each other frequently? Is this frantic chasing or just in play? If they're truly bonded, you should not see any frantic chasing going on and they should mostly tend to sit and flop together or follow one another, in my experience.
