He looks fine for six weeks. Seems to be a hale, healthy boy.
For picking a pup, you should decide what you want in a dog, and have the breeder help you pick a pup. If you want a strong personality ball-of-energy, then that is what you should look for in a pup. If you want a more middle-of-the road, more easy-going personality, than look for that. The breeder who has been with the pups since they were born will know each pup individually waaaaayyyyyy better than you can judge them from pics and one short visit alone.
If you like an over-the-top, confident, high-energy, pushy dog that needs a strong, confident, consistent leader who will be able to meet the dog's mental and physical needs, then this pup might be a good match for you.
If you want something more mellow that will fit in a family structure, get along with other dogs, be eager to please, have a strong pack drive, then choose accordingly.
All puppies are cute, but pictures won't give you the insight you want on making sure you get a puppy that matches your needs and expectations.