I know a fair bit about One World Awards, through QANTAS Frequent Flyer points, so I will concentrate on those.
But based on my experience from other airlines including Star Alliance and Sky Team however I have found most loyalty schemes are very similar.
The points value depends on what you want to buy.
N.B.Values updated to reflect announced changes in June 2019
Worst Value
Buying gifts or gift vouchers is the worst value.
I would get an email every week with offers from the Qantas gift shop to buy luggage, cameras, electrical goods, etc; using my points.
When I check the points against local discount store prices it looks like its around one cent (AU$0.01) for every 2 points.
About the only time I would look at buying something from an airline ‘shop’ would be if the points were set to expire, and I was unable to book a flight,
Better Value
Buying an economy flight with ‘Classic Awards’ is much better value.
Although you will still have to pay Taxes and ‘Carrier Charges’ each point is worth between 1.5 – 2 cents (AU$0.015 – 0.02)
N.B. The points value if using ‘Points plus Pay’ is generally around half the ‘Classic’ award rates (not much better that gifts) although there is better availability of flights.
Best Value
The best value on a strictly points for cash basis is either, buying Higher Class tickets, or asking for an upgrade after buying an economy fare.
The cash equivalent of a point when spent like this can be around 5 cents (AU$0.05)
The problem is that very few Business Class seats are released for Frequent Flyers which makes them fairly hard to get.
At times when I am a higher (Gold) Status it is easier to get upgraded tickets.
Choosing a Flight
I usually choose Qantas as I live in Australia, however I do check the value of the points for the flight so I can compare the overall value with alternative airlines.
Conclusion
Spending points on flying provides the best value.
Understanding the value of points means you can better compare collecting points compared with other discounts you may be offered.