Ummm, well I currently have 2 male dwarfs and chinese and a russian, and I used to have another russian as I bought the two as litter mates, but they fell out very quickly and I woke up one day and one had killed the other
So for dwarfs I would vote girls, unless its a chinese in which case boys have a better temperament. (my boy only bit me once and thats because I scared him.)
I just adopted a syrian girl she sooooo pretty, and she has a lovely temperament, but she was tamed from a young age and has always been handled. So I'll go with girls but not sure tbh.