Milk tea with pearls is the standard and also Chatime's most popular item. But there are so many other great options to choose from.
I recently tried the yogurt lemon tea and found it amazingly refreshing and tart. The brewed Oolong milk tea with pearls and red beans was interesting - the flavour was slightly herbal with a smoky after-taste. I'm happy I got it with no sugar because the red beans add a fair bit of sweetness.
If you don't like to stray too much from the basics, try the roasted milk tea - which adds a slightly stronger flavour to their original milk tea. I had mine with coconut pieces and wasn't disappointed.
Given the high traffic at this location and almost unlimited number of possible drink customizations, service can be understandably slow at times. But you can tell the staff is trying their best to keep up the pace and despite my complicated orders, I always receive very friendly service.