Again…define “best”:

-Best looking
-Best flight characteristics
-Best passenger comfort
-Best maintenance ease/costs
-Best price
-Best safety record
-Best compromise on all criteria…?

Airlines decide “what’s best” in their framework which includes political/nationalistic matters…BEA didn’t buy 727s, United did not buy Tu-154s, and Aeroflot did not buy Tridents.

But today in a free market economy “Best” usually means…which plane will give the airline the best profit margin.