In theory, there are three terms used to describe a male dog these are dog, stud dog and sire. Some people use these names interchangeably; however they do have their own specific and quite definite meanings.
A standard adult, male dog which is not being used for breeding or has not fathered any young tends to be simply known as dog. In the case of those which are to be used in breeding the term given is stud dog as opposed to just dog. Once a dog has fathered a litter of young it can be referred to as sire; this term is not specific to dogs and is instead a general term used in the case of all animals. This is the case whether talking about a pet dog or a wild animal such as a wolf.
Male and female dogs do seem differ slightly in their traits and many people think males make better pets as in the wild it tends to be the female who is more dominant. This seems to have filtered through even into domestic dogs today and it is often apparent that females dogs are more independent, less likely to do what they are told and can be less affectionate. Obviously this isn't true of every female dog, as they each have their own personalities, but as a general rule this seems to be the case. In terms of negatives, a neutered or non-neutered male dog will spray(it's an old myth that spraying will stop when neutered, marking is unrelated to reproduction) and females will go into heat every 6 months for 3-7 days. Both sexes have their pros and cons; these factors should be weighed up before purchasing a dog.