Do I Want an Adult Dog or a Puppy?

From one to three years of age is, in my experience, the most frustrating period for dog owners. Like teenagers, they push their boundaries and try to get away with all sorts of mischief. This is, unsurprisingly, the age that is most often surrendered to shelters by owners that can't take it anymore. Consistency and supervision are the most important things for this stage, even if it means going right back to basic puppy training.

Cons:

Bad Habits From Puppyhood
There might be behaviors that you need to un-train, like counter-surfing, biting, and inappropriate marking, all due to your dog's former life.

Irritating Behaviors
As was mentioned earlier, adolescent dogs will push their boundaries and constantly try to get away with things. It takes a stern leader to get through the adolescent stage, but once you do, the rest is pretty much smooth sailing.

Pick Up Things Fast
Like any sponge, bad can be absorbed along with the good. Once he's learned that something works - whether it's digging in the garbage and he finds a tasty snack, or barking at the door earns him his freedom outside (or back inside), it also stays with him, until you convince him otherwise.

Pros:

The Training Takes Hold
Dogs over a year old have passed the amnesiac stage, and have begun to make connections between behavior and reward, even if that reward is slightly delayed.

At Their Physical Peak
The age-related restrictions on physical exercise have started to lift, allowing to do more strenuous play with your dog, like longer hikes, jogging, jumping games, and starting dog sports if you are so inclined.

A Thirst For Knowledge
A dog just entering his teenage years is a sponge for all things. Training sessions bear fruit much faster, and rules stick in their heads. Now your dog hsas learned what it takes to get the rewards.