
If it were my breed (though all pups are same colour) then it would be considered poor form to book with more than one breeder, as if the breeder you book with has not got enough pups of the sex you booked then they would normally pass you on to another breeder who did, or was expecting their litter after.
As for choice that would depend where in the queue you were. For example you might be third pick dog or Second pick bitch.
Assuming I had 3 bookings of dog and 3 for bitches, then you would know you would be fourth in line and obviously your choice and chances of a pup are less.
You would then decide if you want to be higher up someone elses list for another litter. If I had more pups of one sex than I had bookings chances are that someone else might not have enough, or of course I would have to wait for more sutiable homes. I prefer not to take more than 3 bookings for each sex before pups are born, as I don't like dissapointing folk..