well it is said that a male is more cuddle-bug lap rats then females when they're adults as the general rule but in my experience it really all comes down to the rat. i have one girl, that even from a baby all she ever wanted to do was hang out and chill on me. and i've had boys (though admittedly none older then 5 until just a few days ago) that were always on the go.
but if you were to play odds then finding a lap rat in males would be more likely. remember though, male or female, until they grow up all babies are going to want to play rather then be cuddled unless sleepy.
but if you're getting rats then make sure to get 2 so they can keep each other company. there really is no difference in keeping one as there is keeping 2 but the rats will be happier and healthier.
and if you can afford it you could get one of each gender and either fix both or the other gender. if you go this route and only get one fixed then it is more health benifical to the female though it is often pricer to get done.
and in any case when you do get your rat babies home we want to see pictures! *grins*