if so at what age..is a male dog better?or female dog?
It is not a period, per se, but they will bleed from that area if you do not get them fixed. This usually starts around 6-8 months, and lasts for 21 days every 6 months thereafter. Females can tend to be more aggressive during this time, and if your girl doesn't keep herself very clean by licking it off, then you will end up with blood everywhere. Also, you have to keep guard over them constantly to make sure that no male dogs get to her, otherwise you will have a bunch of innocent baby mutt puppies that you will be responsible for, and there are millions of dogs without homes already.
Males can be more aggressive, and can also spray the house if they are not fixed. As for which is better, these are some of the main problems but it will vary according to each animals individual personality. You could have a very laid back female that is no work, or a male that is a huge mess if not fixed, or vice-versa. There is really no way to tell. Even if they are not fixed their personalities vary so much from dog to dog it really doesn't matter what sex you get.
If you get your dog fixed before they reach adulthood, you will avoid most if not all of these problems. It will also decrease their chance of certain types of cancer and other medical problems. It will save you money in the long run, and you won't have to worry about your pet being injured in the reproductive process, or having to home a litter of puppies that shouldn't have been born. Your female will not have a period, your male shouldn't spray the house. They are usually calmer and happier, and healthier. You can usually get a spay or nueter for less than $100, and if you search there are usually low cost clinics available which are even cheaper. It is the responsible thing to do for your pet, just keep in mind the expense when you figure out how much money you have to pay for the dog, and remember you wil have to pay extra for the spay/nueter, and shots, and if the pup has any health problems.
Hope this helps!