I find this to be a fascinating topic (the PDF is below the YouTube videos) because I completed my graduate studies at Hopkins in biomedical engineering, studying non-viral gene delivery methods. This entailed mainly plasmid and siRNA delivery via polymeric and inorganic nanoparticle delivery modalities. The whole premise behind non-viral gene delivery is that it is safe but more difficult to get effective delivery, in comparison to viruses. Many times we state in the background of these types of articles that they are safer than their viral counterparts. However, associated adenoviruses hit the sweet spot it seems. Assuming somebody does not have antibodies against AAVs, AAVs are generally considered far safer than typical viruses and are effective. I would say the biggest competitor of non-viral gene delivery methods is associated adenoviruses. If I had to bet on products that would be clinically successful, it would be AAV-based products. Fascinating stuff. Here is an interesting YouTube video for non-viral gene delivery by Dr. Banerjee.
Here is an interesting YouTube video for AAVs.