There are two major types of oregano, Mexican and Mediterranean. Mexican oregano is used in Mexican/Hispanic dishes. Mediterranean is used in dishes from that region.
Turkish vs. Greek is a different story. They both grow the same oregano. There may be slight differences created by soil and weather. Mediterranean oregano grown in Turkey is considered the best.
If you're using dry oregano, buy good quality oregano in small quantities (older herbs lose their strength) and you should get the flavor you want.
"If you want to make an apple pie from scratch, you must first create the universe." -Carl Sagan