I use the Outlaws book for English-sounding place names. (especially the "Forest of Dean" section)
I try to avoid Mythic Greece, because of the Demigod stat packages. (A game with a power level that high makes me queasy)
The others are all OK if you are seeking information on a certain culture. I understand that Pirates and At Rapier's Point can be used to make a common campaign setting. However, I prefer pre-gunpowder settings, so I don't use either book.