Every new rat owner wonders if they should get males or females. There are some myths surrounding male rats. The first one is that you cannot keep them together in the same cage because they will fight. This can be true for both sexes. Just like people, some rats just don't like each other. Other than that, rats are social colony animals and prefer to be together. Males can happily live with each other. My 10 boys live in a Critter Nation and I have never had an incident.
Part of your decision should be what you want from your ratties as pets. Do you want really active pets who are always looking for something to do or do you want cuddle bugs that will spend hours watching Netflix with you? If you want action, get girls but if you want couch potatoes, get boys. Now like all things, not every girl will be a ninja warrior and not ever boy will be a potato but generally things go that way. Yes, I know you're thinking...eww... I don't like the boy parts. You get over that quickly if you want snugglers rather than speed runners.