Different breeds of chickens have different comb types. Sounds like the ones you described that had combs are single combed. They are the traditional chicken comb (stands up, has points). The ones you descibed as having no combs are probably peacombs, rosecombs, or walnut combs.
It is almost impossible to sex a chick when they are first hatched. There are people that are specially trained to vent sex (look at their privates, so to speak), but the ordinary person just don't have much luck.
Something that may help you is to try feather sexing. You can look up example pictures online for this. I *think* that if a chick is a female, it gets its wing feathers before a roo. If you pick up a chick and look at the wing feathers:
Roo - "feathers" will look like little toothpicks
Hen- "feathers will be little toothpicks at the wing, but will start fraying out at the ends
Somebody please correct me if I'm wrong!