Generally speaking, I've found that bucks tend to be friendlier, and does can tend to be a bit grumpy. But that is just a generalization as it also can depend on a rabbits individual personality. I've also had does that were extremely lovable and friendly. Your choice of gender will also depend on your future plans as they mature. If you plan on them bonding and staying together, male/female tends to be the best bonding combo, but m/m, f/f can work as well, they just tend to have more problems, and it really all just depends on the individual rabbits personalities, and also if you plan on getting them both fixed. M/F would have to be altered for obvious reasons, and you may be able to get away with m/m f/f without getting them fixed but in most cases it wouldn't work out as they become hormonal, especially the m/m combo, as they often will fight when they become mature and hormonal, and fights can sometimes be vicious. Getting them both fixed is the best thing to do with bonded rabbits, but if you don't plan on doing it, f/f may work and would be your best option in that case. Hormones can totally change rabbits relationships as they mature, so the best thing would be to get an already fixed and bonded pair. It will save you a ton of stress(trust me). Next best would be to get an adult altered rabbit, and find another one that is compatible and seems to get along with the first one. If you get baby buns, just be prepared for the possibility that they may decide they don't like each other when they fully mature, then you will have to keep them in separate cages/pens.