What Greek military hero do you admire most?

[Theodosius the Great]

The only time the Greeks posed an existential threat to Rome was during the Pyrrhic War and during the Hannibalic War when Philip V of Macedonia could have made a difference as Max already stated.

This looks like a good book on the subject: Roman Conquests: Macedonia and Greece

I have the book from this series on the conquest of Italy.

Of course by this stage, all the various Greek city states, regions and kingdoms - throughout the greater Greek world - were pretty much worn out by their endless bickering and internecine strife. In some ways that is why the Romans had it so easy. They only had Carthage to deal with. Had Makedon remained strong and produced another Phillip II or Alexander III - then it might not have been so easy...

Also by this stage the Hellenistic armies were sorely lacking in decent cavalry. This is largely why the manipular legion was superior to the phalanx as it was formed during this period. Even if Macedonia produced another Philip II or Alexander III they would not have had access to the same resources. So, I doubt the Romans would've had much more trouble had this came about.

~Theo