I hardly think it will be a shock to anyone reading this, but according to a recent study in the Journal of Veterinary Behavior, positive training techniques are better than negative methods. Specifically, they promote less stress in the dog, and are better for the dog-person relationship.
A soon-to-be published study called “Effects of 2 training methods on stress-related behaviors of the dog (Canis familiaris) and on the dog-owner relationship”  supports the beliefs of many trainers, behaviorists and guardians that there are substantial advantages to training with positive reinforcement.
In this preliminary study, researchers compared the behavior of dogs being training with positive reinforcement (desired behavior results in the appearance of something positive such as a treat or toy) to those being trained with the use of negative reinforcement (desired behavior results in the disappearance of something negative such as pressure on the leash or body). The data were collected in advanced dog training classes at two different training centers and the behaviors of interest were sitting and walking nicely on a leash.
The dogs being trained with negative reinforcement performed more behaviors that indicate stress in dogs (such as licking their mouths and yawning) and more lowered body postures (the tail down and either the ears lowered or the legs bent in a crouching posture) than dogs being trained with positive reinforcement. The dogs trained with positive reinforcement gazed at their guardians more often than the dogs trained with negative reinforcement. This suggests a stronger connection in those pairs, although the authors acknowledge that those gazes could be a result of dog looking for the reinforcement.
The researchers conclude that positive training techniques are less stressful for dogs and likely better for their well being. This matches my experience with dogs and the people training them. How about you?