The different meds can definitely have different results for an individual. I tried Levitra first and the side effects (headache, nasal in my case) were quite strong while I got virtually no help for ED. I tried Cialis next, same side effects but much milder, and considerably better help on the ED. I haven't tried Viagra.
That being said, do keep in mind that from a nerve recovery viewpoint, you're still fairly early in the process. I was also having much more difficulty in your time frame than I'm having now. Stay positive, and be aware that some patience may be required!