I always have girls. I dont really like the boys for there appearance and the size they get. They get alot bigger and the size scares **** out of me lol. I did once buy 2 adult males which were supposed to be loving. Got them home and in cage no problem. Then they turned nasty, Managed to get one out and it flipped. I rehomed them as there size was to much, have to admit these 2 boys were huge. Ive also been told by male owners that they smell alot also.
The girls ive always had have been very affectionate and sat cuddled with me at night watching tv. One girl wold never leave me alone, always on my shoulder (even when going loo)
I got girls cause they're smaller and sans goolies. Plus they dont' have the buck grease smell, and are more willing to come visit me while I read and then leave and entertain themselves.
But one of mine, Sevilla, I'm sure thinks she's a boy- she'll sit and let me scratch behind her ears as long as I can, and she looooves when I rub up and down her back (stands her short hair on end, it's so cute).
The other one, Belgie, is more "typical" girl, hyper and jumpy and explorative. She likes taking food from me, running away to hide it, and coming back to demand more, walking all over me if she thinks that'll get the job done.
So you can try all you want for what you think a normal example of the gender will be, but just keep an eye out for surpise personalities!
Male rats are WAY less likely to get tumours. So if you don't think you can handle watching your beloved ratties grow huge lumps out of their sides, get males. Four out of the seven girls I've had have gotten tumours.