Oolong teas hold the widest range of flavor and diversity.  They are oxidized between 10-80%.  They are a traditional tea of China and range between green and black tea.  They are generally processed one of two ways by either rolling into curled leaves or pressed into ball-like forms.  Oolong teas are the most complicated to produce and give way to a wide variety of flavors and forms.  Taiwan is well known for its fine Oolongs.