Of the mainstream varieties it's gotta be Yorkshire tea for me; the hard water variety around here.
Black tea, in teabag form, needs milk really unless you have hardcore taste[buds]. In teabags, the tea is ground to small particles to maximise surface area and speed up the brewing process but this will tend to cause a stronger more bitter brew. Milk softens that bitterness.
Purchase a loose leaf black tea that hasn't been ground in any way and the result is usually much more palatable without milk.
Biting the hand that feeds IT
