I think all tea is healthy.
In theory white tea should be healthiest since it is the least processed though green tea is far more researched. In a recent study Oolong tea had a greatest effect increasing metabolism and weight loss with twice the efficacy of green tea.
Black tea gives me cottonmouth so I stick with green and white teas. Except iced tea anyway. Iced tea is diluted enough that iced black tea doesn't give me cottonmouth.
In terms of health, that would be white tea, which is full of antioxidants.