I'm a fan of adult dogs for a variety of reasons. Assuming you go through a rescue, we REALLY try to make sure that the dog is suited to you. We've evaluated the dogs - very thoroughly. I heavily volunteer in GSD rescue, and I'm there almost every day with the dogs. I do basic training with them, exercise, etc. So, I know them really well. As does everyone who works there. We want their next home to be a forever home - so, we make sure they match you.
Which means, with an adult dog, you're probably getting a dog that, at the very least, is house broken and knows some basic commands. You will know his energy level, and his exercise needs. You'll know of any issues, i.e. doesn't like cats, or is ok with cats, etc. His character/temperament is pretty set - so, again, no real surprises.
Plus, an adult dog is A LOT less work than a puppy. I mean, there is an adjustment period (of course). But, after that period - it's all downhill (in a good way).
A puppy is great too. I'm not anti-puppy! My GSD was a puppy when I got him. But, they're a lot of work. It's like having another child.
The best dog for you is the one that will match your needs. You know best what you can handle. If you have the time and energy for a puppy - go for it. If that puppy breed matches your needs/expectations - go for it. If you don't want to live through the puppy years - go for the adult dog, assuming, of course, the lab matches your needs/expectations.