I am also in favor of getting a mutt from a shelter. It's true you can get purebreds from a shelter, but you are much more likely to find a mutt. Mutts generally don't have the problems of purebreds simply because the genetic pool is so mixed. If there are genes that would cause a health issue, they are diluted by genes of other types. Here's a sweeping generalization: Mutts have the best of what each breed in its gene pool has to offer. Of course, dogs, not unlike people, are individuals first and there may be a mutt with a lot of problems. But still, since I'm going to have a pet, not a show dog, I'll go with a shelter mutt every time.
I don't have a dog now, though I used to have dogs, and will probably have one in the future. But my brother has a shepherd mix and she's a great dog!