It's not easy, is it.
But I will have a go.
You know how they often rate Melbourne as the world's most liveable city?
Apparently it is based on surveys-things like access to health, education, housing, services. How satisfied people are with their life/lifestyle.
I would say you also need to look at change in a society & the expansion of the knowledge base.
So.. is the society fairly stable, with law and order? Are most people voluntarily staying put?
Is it a society that has some shared values?
Education and skills are important as they can make life more comfortable and give that society an edge.
Maybe you won't agree with some of these as 'ahead' but I think you have to ask yourself-why, in the last 150 years, did the USA see such a rush of migrants and people wanting 'in' to their society? I would suggest it was because a lot of those migrants saw USA as offering a 'better' life.
If they had to rate the countries, they were in fact putting USA ahead of their own.
Why do we currently have a lot of people trying to get into Australia? Do you ever hear of huge numbers of Aussies trying desperately to get citizenship in Iran/Iraq/Afghanistan? Why not?
Thee are some very politically/socially unstable parts of Africa at the moment. Would you like to go live there, or prefer to stay put?
What about groups that didn't get 'ahead' in science/technology? Was their society necessarily any worse? Take the aboriginals (as they seem to be everyone's fav topic on this forum). I am sure they had stable societies, there were rules, people were probably happy in their communities.
But basic food was sometimes a problem, they got by but had to work at it. And in the end, was the spear or boomerang any match against a gun? Or the sheer numbers of outsiders? I would suggest not.
When we look back at past civilisations, what are some of the things we look at? Not just their beliefs, but their buildings, their innovations, what put them ahead of their rivals.
I'm not necessarily suggesting wealth or knowledge or technology makes for a moral superiority, but stability, a feeling a safety and enough wealth to allow some to tinker with technology & science sure makes for a society people want to live in.
Maybe that is a good enough definition of ahead. A society a lot of people want to live in.
Oh-but ahead also implies some movement/change. can't stay static.