I wouldn't call Gong Cha the best one -- the best bubble tea is from this little shop in Causeway Bay behind Sogo, which I will write about soon -- but you can't beat them for price and consistency.
Gong Cha is like McDonald's: I always know what to expect when I order, and I'm usually not disappointed. I usually have the Taro Milk Tea with Pearl (although I've also tried and enjoyed their Red Bean Milk Tea with Pudding). The pearls are excellent in size and texture: huge, chewy and not slimy at all. I like the pudding because it's more jelly-ish than creamy, but people who like leche flan or creme caramel will probably hate it.
At these places, you order your milk tea base and add on whatever you like: pearls, pudding, red beans, green beans, etc. You can also let them know whether to add more or less syrup and ice. Prices range from HKD12 to HKD20 (or a little more if you keep adding toppings).
Gong Cha has a lot of branches all over Hong Kong. There's one in North Point near the Cantonese opera and there's one in Sheung Wan past Wing On department store on Des Voeux Road right next to a Sheung Wan MTR Station exit (the exit towards Western Market). I forget where exactly the one in Mong Kok is, but it's very conveniently-located. There's also Gong Cha in Causeway Bay, I'm sure.
I like that they also give you a lot of pearls. A bit stingy on the red beans, though.
