Depends the specific circumstance perhaps but I'd go with double blind in the vast majority of situations as it can prove causality. Looking at centuries old worth of evidence surely excedes the 1,000 people population limit you put on the poll...
I totally disagree with the idea of a one size fits all approach to health. There is such a thing as biological individuality.
Sure medical science has raised the average lifespan tremendously, but if you take a look at centenarians they achieve their longevity through clean living. There is a ton of information on what to eat/take for certain effects. I would put a change in diet vs any drug on the market for positive health effects. I don't know of a single drug that has eclipsed a targeted diet change for results.
Nonsense, it's mostly genetic. Centenarians are just as likely as the rest of the population to have what are considered unhealthy lifestyles. http://healthland.time.com/2011/08/05/even-the-long-lived-smoke-drink-and-dont-exercise/