It fluctuates, and also depends on for whom, and if it's relative to ourselves or relative to the rest of the world.
Our starting point was comfortably at the top like 60-75 years ago, and we obviously didn't widen the gap since then, at least for average people, and you could certainly argue we lost the top spot altogether for a lot of segments of society.
Luxuries are still easier to get than anywhere else, but necessities have gotten more difficult. The 50s/60s were probably the "peak", but a lot of that has to do with the fact that a lot of luxuries weren't even an option, so middle class meant the houses were smaller, cars weren't as safe or nice, phones were a shared line with a rotary phone instead of a super computer in every pocket, obviously no computer or internet in the home, no appliances, probably no TV and no cable if you did have one, eating out was a once in a while luxury
Been trending downward. Murka peaked post WW2 and best years were 1945-1980. After Reagan its been trending downwards and had been rated at the level of a developing country for a few years now.
Wait, you think the Vietnam war draft, stagflation and the biggest homicide spike on record in the decade before Reagan took office were some of "the best years"?