The black teas are very bitter and strong. My father likes the loose teas because he has no taste buds
(smoking cigarettes for 42+ years). The dim sum restaurants serve a milder version of this type of tea.
Then you have Chrysanthemum tea, which is light and a little sweet. There is very little after taste and it is usually paired with dim sum dishes. If you are drinking this tea during dim sum, you may request to have sugar added to the tea before it is served. Also, stir the pot to loosen the petals and evenly distribute the sugar.
The purpose of drinking tea during dim sum or any other meal, is the break down of oils from the food for digestion.
Do not drink dietary tea unless you want to lose water weight. You will also be in the bathroom for a very long time, many times over.
Some foreign teas have an exuberant amount of caffeine, so be aware.