[Maximo]

I think there are advantages and disadvantages to both, adding an adult or a puppy.

My second was 8 months and still puppyish, but not full puppy. Some dogs get along great from the start, and others take a little time.

I recommend meeting on neutral territory -- not in either dog's home. Let the dogs greet each other on the floor and don't interfere with elaborate introductions or directions. Intervene only if something looks dangerous. Let the dogs get to know each other and establish the pecking order.

Put your first dog first for everything and make sure he gets lots of attention. Then have activities that both dogs can participate in and focus their attention, like little training sessions.

Best wishes.