Penn-Hip, without a doubt. I know some will disagree, but it is the most reliable and accurate analysis. However, nothing is full-proof.
Many dogs who pass OFA won't pass PennHip, so their proponents logically denounce PennHip.
Another advantage of PennHip is that early detection is available. At 16 weeks, three x-rays are taken by a vet certified in taking such images. The distraction index is measured and calculated, based on the breed. If early signs of hip dysplasia are present, then a JPS procedure can be done at the time of neuter or spay to EASILY prevent exacerbation of the disorder. A tiny portion of the anterior pelvis (the symphysis pubis, about 1 cm at the time for GSDs) is cauterized. This allows the rest of the pelvis to grow "out and over" the femoral heads, providing good coverage.
Now, you can surf the internet and find all kinds of armchair opinions, and even some "official" opinions that sound good. But read the veterinary science literature, if you really want to know. I did (but then, I'm a researcher and science professor with a background in radiologic imaging). I also consulted with a GSD orthopedic specialist. But rather than take my word, go to the library and start reading the actual literature in recent peer-reviewed journals. Much better than getting internet opinions, I think. Then you know what you know for certain.