Unless you wish to breed from your dog or cat neutering is the responsible and recommended choice. As well as protecting from unwanted pregnancies, it will also reducing roaming and behavioural problems.
Spaying your bitch at this age ie .before she has a season will reduce her risk of developing mammary tumours by over  99.5 % .20 % of all entire bitches will develop a life threatening infection of the uterus called a pyometra  and so in spaying your bitch early, this disease can be prevented.Castration of male dogs will prevent testicular and prostatic disease and cancer . Aggression towards other animals is dramatically reduced but the problem may not be eliminated.