Boys tend to be more Territorial and will fight! :/ but two girls will just play with each other i personally think they are both active but if u want more friendliest i would choose the girls! :P good luck! :P
you should get one so that it will want to be with you but if you get 2 they will just like to be together and not care about you also they might not get along
Like almost everyone is saying
Boys are more territorial and will fight more
Girls wont be likely to fight
Gerbils are social animals, so a pair is preferable over just one. Females are the more docile. Males have stronger instincts for territory defense, and can fight over cage space. Males can be housed together, but it is preferred that you are experienced with gerbils and have a large cage for them. If these are your first, a pair of females is the best way to go.
Make sure you know how to sex them before you go into the store. Pet stores are notorious for making sexing errors, and you may just wind up with more unwanted litters.
As a general rule, males of a species are more violent as they fight for dominance. However, it all depends on the actual pet- they each have their own personalities. I'd personally go for two girls. :)