Which of these items is the greatest contributor of obesity?

If these are the kinds of things you're focusing on, then I think you can't see the forest for the trees. Try to "zoom out" your perspective a bit and look at the bigger picture. The greatest contributor to obesity is lifestyle, which is often "inherited" from parents because their children naturally mimic their poor lifestyles. Exacerbating the problem is society's general outlook on obesity, which is that it's a "choice" and therefore the obese deserve to be treated as if they're somehow lesser people because of their weight. You cannot shame people into losing weight. Ironically, this negativity only contributes to the problem as obese people are often MORE drawn to food in an effort to make themselves feel better about the treatment they've received. Food addiction is just as serious, if not more so, as other addictions such as drugs and alcohol. It's actually more difficult in my opinion because at least it's possible to completely rid yourself of drugs and alcohol, whereas everyone must eat to survive. Imagine telling an alcoholic, "well you've got to drink a little bit every day to survive, just don't overdo it." Obese people often have very poor self-esteem as well. The things you mentioned do contribute, but the main issue is mental/emotional.