I think we are living in the best time because of the advances in science, medicine, and technology - also because it seems that humans (certainly not all) are becoming more aware of and less tolerant of things like torture and racism.
It's baffling to me to hear JWs say we're living in the worst time in all history. A few years ago I mentioned that to a couple of elders and told them to go watch a few documentaries on the Middle Ages, the Little Ice Age, the Black Death (plague), etc. and then tell me we're living in the worst time in history. They both looked at me and laughed indicating they got my point and didn't disagree.
I also think we're living on the edge for several reasons. One is the way many societies function now. Consider the U.S. During the Great Depression, many people could still live off the land. They had gardens and chickens. They knew how to can food, etc. Now, most people are dependant on grocery stores and fast food joints, so if something like the Great Depression occurred now, it would be disaster. People can't live off the land now. Many are crowded into areas where there is no available land. If something caused the truckers to stop rolling down the highways, maybe a strike or an economic crash, people would raid the local stores and they would be emptied in a matter of minutes. Consider what middle-class mothers will do at Christmas time to get those desirable gifts that are in short supply; I've seen videos of them turning wild. Imagine how they and others would act if it was food that was needed.
Also, consider the way world economies are so connected now. In the past one economy could collapse and really not affect others, but not so now. For a while a few years ago when the downturn first started, it seemed that the world economy might collapse. If it did, who knows what would happen?
Another thing to consider is population. The earth is a big place but its size is finite, and it can only sustain so many people. The more people, the more pollution and garbage. The more land that is stripped of vegetation. The more rivers that are dammed up. The more fossil fuels that are burned. When I hear people speaking of the need to increase manufacturing to produce jobs, I think the more manufacturing there is, the more stuff there is to throw in landfills. There are areas of ocean covered in floating garbage.
So yeah, I think we're living in the best time, yet at the same time, on the edge.