Different breeds will vary a lot in terms of looks, temperament and personality.
They can be laid back or energetic, guard dogs or family companions and the only thing that medium sized dogs truly have in common is their weight. Consider speaking to a vet to find out what it's really like to own one including any health conditions associated with different breeds.
Compared to small dogs they need more space, access to a garden and more time spent exercising and grooming.
They can live happily in small spaces, but require frequent exercise to help them burn off excess energy. They’re best not left alone for long: if they become bored or restless, they can become very destructive in the home.
Plan to exercise your dog 1-2 hours every day.
Not only do medium dogs take up more space in your house, you need to consider unexpected vet bills too which will be higher the larger your dog. Medium sized dogs will also cost more to feed than smaller dogs. Make sure to choose a complete diet appropriate to their lifestyle and life stage.