Whether or not a dog is going to live a long time and stay healthy depends on the dog. It's not like the pound is buying dogs cut rate from Chinese black market pirate dog dealers. A lot of the time they're the same dogs you would find in pet shops or at the breeders, which got lost, had owners who just couldn't take care of them any more, etc.
I used to breed dogs, so I'm familiar with high quality dogs (which means after five minutes I can tell you all about its health and whether or not its worth adopting and wouldn't go home with a problematic one), and to be honest my last three dogs have all been rescues, and they've been the happiest, friendliest, most loving dogs I've ever had. Not a thing in the world wrong with them.
My only advice would be to foster one first so you can take it home for a week or so and see how it fits in with your life, and to take it to a vet when you decide on one to keep, and have a full check-up and physical done so there aren't any surprises down the road.