Whatever breed you go with, know where the dog comes from...
Talk to the breeder, ask about potential health problems with their dogs, some even keep detailed records of the COI (Coefficient Of Inbreeding - percentage of inbreeding in their line of dogs - try to keep it under 20%), make sure you meet the dam and sire (if available).
This may be the most difficult part - a good breeder will have an application for you to fill out. This application will ask specific questions about your family and the environment that the puppy will be in. The breeder should also perform an LER "Litter Evaluation Report"... what this does is match your preferences for the type of puppy and the environment he/she wil live in to the puppy that best fits your home and your family, and an experienced breeder can choose the best suited pup for you and your family...
I have gotten dogs both ways ... I found the breed of pup I wanted in a classified ad, went to see the pups, and chose the one that I thought would be best for my wife and I. It turned out to be a VERY expensive choice, due to all of the health problems the dog experienced (primarily inherited).
After he had to be put down, I began researching the my next pup (very quiet without one). I found a breeder I was comfortable with that had extensive records of her dogs,and did all of the things I mentioned. I ended up spending a little more money up front to save money later down the line.
Mutts can be great dogs too, but you usually don't have any history on them either
Anyway, good luck with the hunt