That really depends in my opinion. For my taste a strong Assam needs a nice dash of fresh cream and a good amount of sugar, so I would say C2. A fine Darjeeling on the other hand should have no milk/D4, while a cheaper Darjeeling should have a small amount of milk as in D1-2. Earl Grey should always be pure, just with or without sugar, to not drown out the Bergamot aroma, so a clear D4. However, when not using loose tea but tea bags it all doesn’t matter, since the main flavor component will be the paper bag anyway.