I'm not sure that you can ever describe a "greatest generation" from a military point of view. Our service members have a history of doing whatever is required of them, even those who have gone into the service via a draft. Why would we think that our warfighters now are any more or less valorous or capable than those who have gone before (or vice versa)?
I do think from a technology/econometric point of view, one could argue for a "greatest generation." Those who were of the age to fight in or lead fighters in WWII:
- overcame the economic horror of the Great Depression to generate the greatest economic power in the world
- in the process, the "Arsenal of Democracy" produced trucks, tanks, aircraft, and other war materiel to support British and Russian troops in addition to the largest US military force in history
- For better or for worse, the same generation made many truly revolutionary technological developments: the first widespread use of penicillin; development of radar, sonar, analog computers; atomic weapons, leading us to nuke power; jet engines & aircraft; rocketry; spacecraft/satellites, including the Apollo moon landing; TV; the structure of DNA; integrated circuits. Note that a lot of these inventions were not made by Americans.