I Agree with Clodius, the X Legion was probably the most famous legion and most sucessful. I say this because their victories were numerous and quite well known. The legion also lasted numerous Emperors. They helped defeat Gaul, fought against the Germans, invaded britain with Caesar, were the spearhed for Caesar's campaign and battles agaisnt Pompey in the Civil war including Pharsalus,Campaigned in North Africa, fought against the murderers of Caesar at Phillipi, fought agaisnt Marka antony at Actium, fought against Rome's age old enemy the Parthians in Armenia, Took the city of Jerusalem (famous siege of Jerusalem), and finally took the great fortress of Masada in Judea.
One example of their skill is their siege of the strong Parthian fortress of Volandum. In the storming of the fort they didnt lose a singe legionary, and only a handful were wounded.
You cant get much better than that.